diff --git a/src/core/identity-db.ts b/src/core/identity-db.ts
index c802a19..1500c7d 100644
--- a/src/core/identity-db.ts
+++ b/src/core/identity-db.ts
@@ -1,39 +1,27 @@
 import {
+  type AddFactInput,
   type ConnectedTopic,
   type Fact,
   type FactTopic,
   type FindSimilarFactsInput,
   type IndexFactEmbeddingsInput,
+  type LinkTopicsInput,
   type ListTopicsOptions,
   type ScoredFact,
   type SearchFactsInput,
+  type Space,
+  type SpaceScopedInput,
   type Topic,
   type TopicLookupOptions,
   type TopicWithFacts,
+  type UpsertSpaceInput,
   type UpsertTopicInput,
-  type AddFactInput,
-  type LinkTopicsInput,
 } from '../types/api';
 import type { IngestStatementOptions } from '../ingestion/types';
 import type { DatabaseConnection, IdentityDBConnectionConfig } from '../adapters/dialect';
 import type { IdentityDatabaseSchema } from '../types/database';
-import type { FactRecord, TopicRecord } from '../types/domain';
+import type { FactRecord, SpaceRecord, TopicRecord } from '../types/domain';
 import { createDatabase } from '../adapters/dialect';
-import { IdentityDBError } from './errors';
-import { initializeSchema } from './migrations';
-import {
-  canonicalizeTopicName,
-  cosineSimilarity,
-  createContentHash,
-  createId,
-  deserializeEmbedding,
-  mapFactRow,
-  mapTopicRow,
-  normalizeTopicName,
-  nowIsoString,
-  serializeEmbedding,
-  serializeMetadata,
-} from './utils';
 import { extractFact } from '../ingestion/extractor';
 import {
   findFactRowsConnectingTopicIds,
@@ -41,16 +29,37 @@ import {
   findTopicLinksForFactIds,
 } from '../queries/facts';
 import {
+  type DatabaseExecutor,
+  findChildTopicRows,
   findConnectedTopicRows,
+  findParentTopicRows,
+  findSpaceRowByNormalizedName,
   findTopicRowByNameOrAlias,
   findTopicRowByNormalizedAlias,
   findTopicRowByNormalizedName,
   listTopicAliasRowsForTopicId,
   listTopicRows,
-  findChildTopicRows,
-  findParentTopicRows,
-  type DatabaseExecutor,
 } from '../queries/topics';
+import { IdentityDBError } from './errors';
+import { initializeSchema } from './migrations';
+import {
+  canonicalizeSpaceName,
+  canonicalizeTopicName,
+  cosineSimilarity,
+  createContentHash,
+  createId,
+  deserializeEmbedding,
+  mapFactRow,
+  mapSpaceRow,
+  mapTopicRow,
+  normalizeSpaceName,
+  normalizeTopicName,
+  nowIsoString,
+  serializeEmbedding,
+  serializeMetadata,
+} from './utils';
+
+const DEFAULT_SPACE_NAME = 'default';
 
 export class IdentityDB {
   private constructor(private readonly connection: DatabaseConnection) {}
@@ -68,6 +77,72 @@ export class IdentityDB {
     await this.connection.destroy();
   }
 
+  async upsertSpace(input: UpsertSpaceInput): Promise<Space> {
+    return this.connection.db.transaction().execute(async (trx) => {
+      const normalizedName = normalizeSpaceName(input.name);
+      if (normalizedName.length === 0) {
+        throw new IdentityDBError('Space name cannot be empty.');
+      }
+
+      const now = nowIsoString();
+      const existing = await findSpaceRowByNormalizedName(trx, normalizedName);
+
+      if (existing) {
+        await trx
+          .updateTable('spaces')
+          .set({
+            name: canonicalizeSpaceName(input.name),
+            description: input.description !== undefined ? input.description : existing.description,
+            metadata: input.metadata !== undefined ? serializeMetadata(input.metadata) : existing.metadata,
+            updated_at: now,
+          })
+          .where('id', '=', existing.id)
+          .execute();
+
+        const updated = await trx
+          .selectFrom('spaces')
+          .selectAll()
+          .where('id', '=', existing.id)
+          .executeTakeFirstOrThrow();
+
+        return mapSpaceRow(updated);
+      }
+
+      const createdRow: SpaceRecord = {
+        id: createId(),
+        name: canonicalizeSpaceName(input.name),
+        normalized_name: normalizedName,
+        description: input.description ?? null,
+        metadata: serializeMetadata(input.metadata),
+        created_at: now,
+        updated_at: now,
+      };
+
+      await trx.insertInto('spaces').values(createdRow).execute();
+      return mapSpaceRow(createdRow);
+    });
+  }
+
+  async getSpaceByName(name: string): Promise<Space | null> {
+    const normalizedName = normalizeSpaceName(name);
+    if (normalizedName.length === 0) {
+      return null;
+    }
+
+    const row = await findSpaceRowByNormalizedName(this.connection.db, normalizedName);
+    return row ? mapSpaceRow(row) : null;
+  }
+
+  async listSpaces(): Promise<Space[]> {
+    const rows = await this.connection.db
+      .selectFrom('spaces')
+      .selectAll()
+      .orderBy('normalized_name', 'asc')
+      .execute();
+
+    return rows.map(mapSpaceRow);
+  }
+
   async upsertTopic(input: UpsertTopicInput): Promise<Topic> {
     return this.upsertTopicInExecutor(this.connection.db, input);
   }
@@ -82,6 +157,7 @@ export class IdentityDB {
     }
 
     return this.connection.db.transaction().execute(async (trx) => {
+      const space = await this.getOrCreateSpaceInExecutor(trx, input.spaceName);
       const createdAt = nowIsoString();
       const factId = createId();
 
@@ -89,6 +165,7 @@ export class IdentityDB {
         .insertInto('facts')
         .values({
           id: factId,
+          space_id: space.id,
           statement: input.statement.trim(),
           summary: input.summary ?? null,
           source: input.source ?? null,
@@ -103,7 +180,11 @@ export class IdentityDB {
 
       for (let index = 0; index < input.topics.length; index += 1) {
         const topicInput = input.topics[index]!;
-        const topic = await this.upsertTopicInExecutor(trx, topicInput);
+        this.assertScopedTopicInput(space, topicInput.spaceName);
+        const topic = await this.upsertTopicInExecutor(trx, {
+          ...topicInput,
+          spaceName: space.name,
+        });
 
         await trx
           .insertInto('fact_topics')
@@ -125,6 +206,7 @@ export class IdentityDB {
 
       return {
         id: factId,
+        spaceId: space.id,
         statement: input.statement.trim(),
         summary: input.summary ?? null,
         source: input.source ?? null,
@@ -137,14 +219,12 @@ export class IdentityDB {
     });
   }
 
-  async ingestStatement(
-    statement: string,
-    options: IngestStatementOptions,
-  ): Promise<Fact> {
+  async ingestStatement(statement: string, options: IngestStatementOptions): Promise<Fact> {
     const extracted = await extractFact(statement, options.extractor);
     const factInput: AddFactInput = {
       statement: extracted.statement ?? statement,
       topics: extracted.topics,
+      spaceName: options.spaceName,
     };
 
     if (extracted.summary !== undefined) {
@@ -170,6 +250,7 @@ export class IdentityDB {
         topicNames: factInput.topics.map((topic) => topic.name),
         limit: 1,
         minimumScore: options.duplicateThreshold ?? 0.97,
+        spaceName: options.spaceName,
       });
 
       if (similarFacts[0]) {
@@ -180,15 +261,27 @@ export class IdentityDB {
     const fact = await this.addFact(factInput);
 
     if (options.embeddingProvider) {
-      await this.indexFactEmbedding(fact.id, { provider: options.embeddingProvider });
+      await this.indexFactEmbedding(fact.id, {
+        provider: options.embeddingProvider,
+        spaceName: options.spaceName,
+      });
     }
 
     return fact;
   }
 
   async indexFactEmbeddings(input: IndexFactEmbeddingsInput): Promise<void> {
-    const factRows = await this.connection.db.selectFrom('facts').selectAll().orderBy('created_at', 'asc').execute();
+    const space = await this.getSpaceForRead(input.spaceName);
+    if (input.spaceName && !space) {
+      return;
+    }
 
+    let factQuery = this.connection.db.selectFrom('facts').selectAll().orderBy('created_at', 'asc');
+    if (space) {
+      factQuery = factQuery.where('space_id', '=', space.id);
+    }
+
+    const factRows = await factQuery.execute();
     if (factRows.length === 0) {
       return;
     }
@@ -222,6 +315,13 @@ export class IdentityDB {
       throw new IdentityDBError(`Fact not found: ${factId}`);
     }
 
+    if (input.spaceName) {
+      const space = await this.getSpaceForRead(input.spaceName);
+      if (!space || space.id !== factRow.space_id) {
+        throw new IdentityDBError(`Fact ${factId} does not belong to space ${canonicalizeSpaceName(input.spaceName)}.`);
+      }
+    }
+
     const embedding = await input.provider.embed(factRow.statement);
     this.assertEmbeddingShape(embedding, input.provider.dimensions);
 
@@ -236,6 +336,11 @@ export class IdentityDB {
       return [];
     }
 
+    const space = await this.getSpaceForRead(input.spaceName);
+    if (input.spaceName && !space) {
+      return [];
+    }
+
     const queryEmbedding = await input.provider.embed(queryText);
     this.assertEmbeddingShape(queryEmbedding, input.provider.dimensions);
 
@@ -245,6 +350,7 @@ export class IdentityDB {
       topicNames: input.topicNames,
       limit: input.limit,
       minimumScore: input.minimumScore,
+      spaceId: space?.id,
     });
   }
 
@@ -254,6 +360,11 @@ export class IdentityDB {
       return [];
     }
 
+    const space = await this.getSpaceForRead(input.spaceName);
+    if (input.spaceName && !space) {
+      return [];
+    }
+
     const queryEmbedding = await input.provider.embed(statement);
     this.assertEmbeddingShape(queryEmbedding, input.provider.dimensions);
 
@@ -263,6 +374,7 @@ export class IdentityDB {
       topicNames: input.topicNames,
       limit: input.limit,
       minimumScore: input.minimumScore,
+      spaceId: space?.id,
     });
   }
 
@@ -279,12 +391,15 @@ export class IdentityDB {
     }
 
     await this.connection.db.transaction().execute(async (trx) => {
+      const space = await this.getOrCreateSpaceInExecutor(trx, input.spaceName);
       const parentTopic = await this.upsertTopicInExecutor(trx, {
         name: input.parentName,
         granularity: 'abstract',
+        spaceName: space.name,
       });
       const childTopic = await this.upsertTopicInExecutor(trx, {
         name: input.childName,
+        spaceName: space.name,
       });
 
       const existing = await trx
@@ -309,7 +424,7 @@ export class IdentityDB {
     });
   }
 
-  async addTopicAlias(canonicalName: string, alias: string): Promise<void> {
+  async addTopicAlias(canonicalName: string, alias: string, options?: SpaceScopedInput): Promise<void> {
     const normalizedAlias = normalizeTopicName(alias);
 
     if (normalizedAlias.length === 0) {
@@ -317,18 +432,22 @@ export class IdentityDB {
     }
 
     await this.connection.db.transaction().execute(async (trx) => {
-      const canonicalTopic = await this.upsertTopicInExecutor(trx, { name: canonicalName });
+      const space = await this.getOrCreateSpaceInExecutor(trx, options?.spaceName);
+      const canonicalTopic = await this.upsertTopicInExecutor(trx, {
+        name: canonicalName,
+        spaceName: space.name,
+      });
 
       if (normalizedAlias === canonicalTopic.normalizedName) {
         return;
       }
 
-      const exactTopicMatch = await findTopicRowByNormalizedName(trx, normalizedAlias);
+      const exactTopicMatch = await findTopicRowByNormalizedName(trx, space.id, normalizedAlias);
       if (exactTopicMatch && exactTopicMatch.id !== canonicalTopic.id) {
         throw new IdentityDBError('Cannot assign an alias that already belongs to another canonical topic.');
       }
 
-      const aliasMatch = await findTopicRowByNormalizedAlias(trx, normalizedAlias);
+      const aliasMatch = await findTopicRowByNormalizedAlias(trx, space.id, normalizedAlias);
       if (aliasMatch) {
         if (aliasMatch.id !== canonicalTopic.id) {
           throw new IdentityDBError('Cannot assign an alias that already resolves to another topic.');
@@ -341,6 +460,7 @@ export class IdentityDB {
         .insertInto('topic_aliases')
         .values({
           id: createId(),
+          space_id: space.id,
           topic_id: canonicalTopic.id,
           alias: canonicalizeTopicName(alias),
           normalized_alias: normalizedAlias,
@@ -352,47 +472,43 @@ export class IdentityDB {
     });
   }
 
-  async resolveTopic(name: string): Promise<Topic | null> {
-    const topicRow = await this.getRequiredTopicRow(name);
+  async resolveTopic(name: string, options?: SpaceScopedInput): Promise<Topic | null> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     return topicRow ? mapTopicRow(topicRow) : null;
   }
 
-  async getTopicAliases(name: string): Promise<string[]> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async getTopicAliases(name: string, options?: SpaceScopedInput): Promise<string[]> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return [];
     }
 
-    const aliasRows = await listTopicAliasRowsForTopicId(this.connection.db, topicRow.id);
+    const aliasRows = await listTopicAliasRowsForTopicId(this.connection.db, topicRow.space_id, topicRow.id);
     return aliasRows.map((aliasRow) => aliasRow.alias);
   }
 
-  async getTopicChildren(name: string): Promise<Topic[]> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async getTopicChildren(name: string, options?: SpaceScopedInput): Promise<Topic[]> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return [];
     }
 
-    const childRows = await findChildTopicRows(this.connection.db, topicRow.id);
+    const childRows = await findChildTopicRows(this.connection.db, topicRow.space_id, topicRow.id);
     return childRows.map(mapTopicRow);
   }
 
-  async getTopicParents(name: string): Promise<Topic[]> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async getTopicParents(name: string, options?: SpaceScopedInput): Promise<Topic[]> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return [];
     }
 
-    const parentRows = await findParentTopicRows(this.connection.db, topicRow.id);
+    const parentRows = await findParentTopicRows(this.connection.db, topicRow.space_id, topicRow.id);
     return parentRows.map(mapTopicRow);
   }
 
-  async getTopicLineage(name: string): Promise<Topic[]> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async getTopicLineage(name: string, options?: SpaceScopedInput): Promise<Topic[]> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return [];
     }
@@ -405,8 +521,7 @@ export class IdentityDB {
       const nextLevelIds: string[] = [];
 
       for (const currentId of currentLevelIds) {
-        const parentRows = await findParentTopicRows(this.connection.db, currentId);
-
+        const parentRows = await findParentTopicRows(this.connection.db, topicRow.space_id, currentId);
         for (const parentRow of parentRows) {
           if (visitedTopicIds.has(parentRow.id)) {
             continue;
@@ -424,97 +539,97 @@ export class IdentityDB {
     return lineage;
   }
 
-  async getTopicFacts(name: string): Promise<Fact[]> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async getTopicFacts(name: string, options?: SpaceScopedInput): Promise<Fact[]> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return [];
     }
 
-    const factRows = await findFactRowsForTopicId(this.connection.db, topicRow.id);
-    return this.hydrateFacts(factRows);
+    const factRows = await findFactRowsForTopicId(this.connection.db, topicRow.space_id, topicRow.id);
+    return this.hydrateFacts(factRows, topicRow.space_id);
   }
 
-  async getTopicFactsLinkedTo(name: string, linkedTopicName: string): Promise<Fact[]> {
-    return this.findFactsConnectingTopics([name, linkedTopicName]);
+  async getTopicFactsLinkedTo(name: string, linkedTopicName: string, options?: SpaceScopedInput): Promise<Fact[]> {
+    return this.findFactsConnectingTopics([name, linkedTopicName], options);
   }
 
-  async findFactsConnectingTopics(names: string[]): Promise<Fact[]> {
+  async findFactsConnectingTopics(names: string[], options?: SpaceScopedInput): Promise<Fact[]> {
     if (names.length === 0) {
       return [];
     }
 
-    const topicRows = await Promise.all(names.map((name) => this.getRequiredTopicRow(name)));
+    const space = await this.getSpaceForRead(options?.spaceName);
+    if (options?.spaceName && !space) {
+      return [];
+    }
 
+    const topicRows = await Promise.all(names.map((name) => this.getRequiredTopicRow(name, options?.spaceName)));
     if (topicRows.some((topicRow) => topicRow === undefined)) {
       return [];
     }
 
     const topicIds = topicRows.map((topicRow) => topicRow!.id);
-    const factRows = await findFactRowsConnectingTopicIds(this.connection.db, topicIds);
+    const spaceId = topicRows[0]!.space_id ?? space?.id;
+    const factRows = await findFactRowsConnectingTopicIds(this.connection.db, spaceId, topicIds);
 
-    return this.hydrateFacts(factRows);
+    return this.hydrateFacts(factRows, spaceId);
   }
 
-  async getTopicByName(
-    name: string,
-    options: { includeFacts: true },
-  ): Promise<TopicWithFacts | null>;
+  async getTopicByName(name: string, options: { includeFacts: true; spaceName?: string }): Promise<TopicWithFacts | null>;
   async getTopicByName(name: string, options?: TopicLookupOptions): Promise<Topic | null>;
-  async getTopicByName(
-    name: string,
-    options?: TopicLookupOptions,
-  ): Promise<Topic | TopicWithFacts | null> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async getTopicByName(name: string, options?: TopicLookupOptions): Promise<Topic | TopicWithFacts | null> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return null;
     }
 
     const topic = mapTopicRow(topicRow);
-
     if (options?.includeFacts) {
       return {
         ...topic,
-        facts: await this.getTopicFacts(name),
+        facts: await this.getTopicFacts(name, { spaceName: options.spaceName }),
       };
     }
 
     return topic;
   }
 
-  async listTopics(options: { includeFacts: true; limit?: number }): Promise<TopicWithFacts[]>;
+  async listTopics(options: { includeFacts: true; limit?: number; spaceName?: string }): Promise<TopicWithFacts[]>;
   async listTopics(options?: ListTopicsOptions): Promise<Topic[]>;
-  async listTopics(
-    options?: ListTopicsOptions,
-  ): Promise<Topic[] | TopicWithFacts[]> {
-    const rows = await listTopicRows(this.connection.db, options?.limit);
+  async listTopics(options?: ListTopicsOptions): Promise<Topic[] | TopicWithFacts[]> {
+    const space = await this.getSpaceForRead(options?.spaceName);
+    if (options?.spaceName && !space) {
+      return [];
+    }
 
+    const spaceId = space?.id ?? await this.getDefaultSpaceIdForRead();
+    if (!spaceId) {
+      return [];
+    }
+
+    const rows = await listTopicRows(this.connection.db, spaceId, options?.limit);
     if (!options?.includeFacts) {
       return rows.map(mapTopicRow);
     }
 
     const topicsWithFacts: TopicWithFacts[] = [];
-
     for (const row of rows) {
       topicsWithFacts.push({
         ...mapTopicRow(row),
-        facts: await this.getTopicFacts(row.name),
+        facts: await this.getTopicFacts(row.name, { spaceName: options?.spaceName }),
       });
     }
 
     return topicsWithFacts;
   }
 
-  async findConnectedTopics(name: string): Promise<ConnectedTopic[]> {
-    const topicRow = await this.getRequiredTopicRow(name);
-
+  async findConnectedTopics(name: string, options?: SpaceScopedInput): Promise<ConnectedTopic[]> {
+    const topicRow = await this.getRequiredTopicRow(name, options?.spaceName);
     if (!topicRow) {
       return [];
     }
 
-    const rows = await findConnectedTopicRows(this.connection.db, topicRow.id);
-
+    const rows = await findConnectedTopicRows(this.connection.db, topicRow.space_id, topicRow.id);
     return rows.map((row) => ({
       ...mapTopicRow(row),
       sharedFactCount: row.shared_fact_count,
@@ -527,18 +642,25 @@ export class IdentityDB {
     topicNames?: string[] | undefined;
     limit?: number | undefined;
     minimumScore?: number | undefined;
+    spaceId?: string | undefined;
   }): Promise<ScoredFact[]> {
-    const topicIds = await this.resolveTopicIds(input.topicNames);
+    const effectiveSpaceId = input.spaceId ?? await this.getDefaultSpaceIdForRead();
+    if (!effectiveSpaceId) {
+      return [];
+    }
+
+    const topicIds = await this.resolveTopicIds(input.topicNames, effectiveSpaceId);
     if (topicIds === null) {
       return [];
     }
 
     const factRows = topicIds.length > 0
-      ? await findFactRowsConnectingTopicIds(this.connection.db, topicIds)
+      ? await findFactRowsConnectingTopicIds(this.connection.db, effectiveSpaceId, topicIds)
       : await this.connection.db
           .selectFrom('facts')
           .innerJoin('fact_embeddings', 'fact_embeddings.fact_id', 'facts.id')
           .selectAll('facts')
+          .where('facts.space_id', '=', effectiveSpaceId)
           .where('fact_embeddings.model', '=', input.providerModel)
           .orderBy('facts.created_at', 'asc')
           .execute();
@@ -547,14 +669,14 @@ export class IdentityDB {
       return [];
     }
 
-    const embeddingRowsQuery = this.connection.db
+    const embeddingRows = await this.connection.db
       .selectFrom('fact_embeddings')
-      .selectAll()
-      .where('model', '=', input.providerModel);
-
-    const embeddingRows = factRows.length > 0
-      ? await embeddingRowsQuery.where('fact_id', 'in', factRows.map((factRow) => factRow.id)).execute()
-      : [];
+      .innerJoin('facts', 'facts.id', 'fact_embeddings.fact_id')
+      .selectAll('fact_embeddings')
+      .where('facts.space_id', '=', effectiveSpaceId)
+      .where('fact_embeddings.model', '=', input.providerModel)
+      .where('fact_embeddings.fact_id', 'in', factRows.map((factRow) => factRow.id))
+      .execute();
 
     const embeddingsByFactId = new Map(
       embeddingRows.map((embeddingRow) => [embeddingRow.fact_id, deserializeEmbedding(embeddingRow.embedding)]),
@@ -578,7 +700,7 @@ export class IdentityDB {
       return [];
     }
 
-    const hydratedFacts = await this.hydrateFacts(scoredRows.map((entry) => entry.factRow));
+    const hydratedFacts = await this.hydrateFacts(scoredRows.map((entry) => entry.factRow), effectiveSpaceId);
     const factsById = new Map(hydratedFacts.map((fact) => [fact.id, fact]));
 
     return scoredRows.map((entry) => ({
@@ -587,12 +709,12 @@ export class IdentityDB {
     }));
   }
 
-  private async resolveTopicIds(topicNames?: string[]): Promise<string[] | null> {
+  private async resolveTopicIds(topicNames: string[] | undefined, spaceId: string): Promise<string[] | null> {
     if (!topicNames || topicNames.length === 0) {
       return [];
     }
 
-    const topicRows = await Promise.all(topicNames.map((topicName) => this.getRequiredTopicRow(topicName)));
+    const topicRows = await Promise.all(topicNames.map((topicName) => this.getRequiredTopicRowInSpaceId(topicName, spaceId)));
     if (topicRows.some((topicRow) => !topicRow)) {
       return null;
     }
@@ -637,30 +759,28 @@ export class IdentityDB {
     }
   }
 
-  private async upsertTopicInExecutor(
-    executor: DatabaseExecutor,
-    input: UpsertTopicInput,
-  ): Promise<Topic> {
+  private async upsertTopicInExecutor(executor: DatabaseExecutor, input: UpsertTopicInput): Promise<Topic> {
     const normalizedName = normalizeTopicName(input.name);
-
     if (normalizedName.length === 0) {
       throw new IdentityDBError('Topic name cannot be empty.');
     }
 
-    const existing = await findTopicRowByNormalizedName(executor, normalizedName);
+    const space = await this.getOrCreateSpaceInExecutor(executor, input.spaceName);
+    const existing = await findTopicRowByNormalizedName(executor, space.id, normalizedName);
     const now = nowIsoString();
 
     if (existing) {
       return this.updateTopicRowInExecutor(executor, existing, input, now, true);
     }
 
-    const aliasedTopic = await findTopicRowByNormalizedAlias(executor, normalizedName);
+    const aliasedTopic = await findTopicRowByNormalizedAlias(executor, space.id, normalizedName);
     if (aliasedTopic) {
       return this.updateTopicRowInExecutor(executor, aliasedTopic, input, now, false);
     }
 
     const createdRow: TopicRecord = {
       id: createId(),
+      space_id: space.id,
       name: canonicalizeTopicName(input.name),
       normalized_name: normalizedName,
       category: input.category ?? 'custom',
@@ -672,7 +792,6 @@ export class IdentityDB {
     };
 
     await executor.insertInto('topics').values(createdRow).execute();
-
     return mapTopicRow(createdRow);
   }
 
@@ -705,22 +824,39 @@ export class IdentityDB {
     return mapTopicRow(updated);
   }
 
-  private async getRequiredTopicRow(name: string): Promise<TopicRecord | undefined> {
-    const normalizedName = normalizeTopicName(name);
+  private async getRequiredTopicRow(name: string, spaceName?: string): Promise<TopicRecord | undefined> {
+    const space = await this.getSpaceForRead(spaceName);
+    if (spaceName && !space) {
+      return undefined;
+    }
 
+    const spaceId = space?.id ?? await this.getDefaultSpaceIdForRead();
+    if (!spaceId) {
+      return undefined;
+    }
+
+    return this.getRequiredTopicRowInSpaceId(name, spaceId);
+  }
+
+  private async getRequiredTopicRowInSpaceId(name: string, spaceId: string): Promise<TopicRecord | undefined> {
+    const normalizedName = normalizeTopicName(name);
     if (normalizedName.length === 0) {
       return undefined;
     }
 
-    return findTopicRowByNameOrAlias(this.connection.db, normalizedName);
+    return findTopicRowByNameOrAlias(this.connection.db, spaceId, normalizedName);
   }
 
-  private async hydrateFacts(factRows: FactRecord[]): Promise<Fact[]> {
+  private async hydrateFacts(factRows: FactRecord[], spaceId?: string): Promise<Fact[]> {
+    if (factRows.length === 0) {
+      return [];
+    }
+
+    const effectiveSpaceId = spaceId ?? factRows[0]!.space_id;
     const factIds = factRows.map((fact) => fact.id);
-    const topicLinks = await findTopicLinksForFactIds(this.connection.db, factIds);
+    const topicLinks = await findTopicLinksForFactIds(this.connection.db, effectiveSpaceId, factIds);
 
     const topicsByFactId = new Map<string, FactTopic[]>();
-
     for (const topicLink of topicLinks) {
       const topics = topicsByFactId.get(topicLink.fact_id) ?? [];
       topics.push({
@@ -733,4 +869,57 @@ export class IdentityDB {
 
     return factRows.map((factRow) => mapFactRow(factRow, topicsByFactId.get(factRow.id) ?? []));
   }
+
+  private async getOrCreateSpaceInExecutor(executor: DatabaseExecutor, requestedSpaceName?: string): Promise<SpaceRecord> {
+    const normalizedName = normalizeSpaceName(requestedSpaceName ?? DEFAULT_SPACE_NAME);
+    const canonicalName = canonicalizeSpaceName(requestedSpaceName ?? DEFAULT_SPACE_NAME);
+    const existing = await findSpaceRowByNormalizedName(executor, normalizedName);
+    if (existing) {
+      return existing;
+    }
+
+    const now = nowIsoString();
+    const createdRow: SpaceRecord = {
+      id: createId(),
+      name: canonicalName,
+      normalized_name: normalizedName,
+      description: null,
+      metadata: null,
+      created_at: now,
+      updated_at: now,
+    };
+
+    await executor.insertInto('spaces').values(createdRow).execute();
+    return createdRow;
+  }
+
+  private async getSpaceForRead(spaceName?: string): Promise<SpaceRecord | undefined> {
+    if (!spaceName) {
+      return undefined;
+    }
+
+    const normalizedName = normalizeSpaceName(spaceName);
+    if (normalizedName.length === 0) {
+      return undefined;
+    }
+
+    return findSpaceRowByNormalizedName(this.connection.db, normalizedName);
+  }
+
+  private async getDefaultSpaceIdForRead(): Promise<string | undefined> {
+    const defaultSpace = await findSpaceRowByNormalizedName(this.connection.db, normalizeSpaceName(DEFAULT_SPACE_NAME));
+    return defaultSpace?.id;
+  }
+
+  private assertScopedTopicInput(space: SpaceRecord, topicSpaceName?: string): void {
+    if (!topicSpaceName) {
+      return;
+    }
+
+    if (normalizeSpaceName(topicSpaceName) !== space.normalized_name) {
+      throw new IdentityDBError(
+        `Fact topics cannot point to a different space than the fact itself (${space.name}).`,
+      );
+    }
+  }
 }
diff --git a/src/core/migrations.ts b/src/core/migrations.ts
index 2bc2398..d95629e 100644
--- a/src/core/migrations.ts
+++ b/src/core/migrations.ts
@@ -4,6 +4,7 @@ import {
   FACTS_TABLE,
   FACT_EMBEDDINGS_TABLE,
   FACT_TOPICS_TABLE,
+  SPACES_TABLE,
   TOPIC_ALIASES_TABLE,
   TOPIC_RELATIONS_TABLE,
   TOPICS_TABLE,
@@ -14,23 +15,42 @@ export async function initializeSchema(
   db: Kysely<IdentityDatabaseSchema>,
 ): Promise<void> {
   await db.schema
-    .createTable(TOPICS_TABLE)
+    .createTable(SPACES_TABLE)
     .ifNotExists()
     .addColumn('id', 'text', (column) => column.primaryKey())
     .addColumn('name', 'text', (column) => column.notNull())
     .addColumn('normalized_name', 'text', (column) => column.notNull().unique())
-    .addColumn('category', 'text', (column) => column.notNull())
-    .addColumn('granularity', 'text', (column) => column.notNull())
     .addColumn('description', 'text')
     .addColumn('metadata', 'text')
     .addColumn('created_at', 'text', (column) => column.notNull())
     .addColumn('updated_at', 'text', (column) => column.notNull())
     .execute();
 
+  await db.schema
+    .createTable(TOPICS_TABLE)
+    .ifNotExists()
+    .addColumn('id', 'text', (column) => column.primaryKey())
+    .addColumn('space_id', 'text', (column) =>
+      column.notNull().references(`${SPACES_TABLE}.id`).onDelete('cascade'),
+    )
+    .addColumn('name', 'text', (column) => column.notNull())
+    .addColumn('normalized_name', 'text', (column) => column.notNull())
+    .addColumn('category', 'text', (column) => column.notNull())
+    .addColumn('granularity', 'text', (column) => column.notNull())
+    .addColumn('description', 'text')
+    .addColumn('metadata', 'text')
+    .addColumn('created_at', 'text', (column) => column.notNull())
+    .addColumn('updated_at', 'text', (column) => column.notNull())
+    .addUniqueConstraint('topics_space_normalized_name_key', ['space_id', 'normalized_name'])
+    .execute();
+
   await db.schema
     .createTable(FACTS_TABLE)
     .ifNotExists()
     .addColumn('id', 'text', (column) => column.primaryKey())
+    .addColumn('space_id', 'text', (column) =>
+      column.notNull().references(`${SPACES_TABLE}.id`).onDelete('cascade'),
+    )
     .addColumn('statement', 'text', (column) => column.notNull())
     .addColumn('summary', 'text')
     .addColumn('source', 'text')
@@ -88,14 +108,32 @@ export async function initializeSchema(
     .createTable(TOPIC_ALIASES_TABLE)
     .ifNotExists()
     .addColumn('id', 'text', (column) => column.primaryKey())
+    .addColumn('space_id', 'text', (column) =>
+      column.notNull().references(`${SPACES_TABLE}.id`).onDelete('cascade'),
+    )
     .addColumn('topic_id', 'text', (column) =>
       column.notNull().references(`${TOPICS_TABLE}.id`).onDelete('cascade'),
     )
     .addColumn('alias', 'text', (column) => column.notNull())
-    .addColumn('normalized_alias', 'text', (column) => column.notNull().unique())
+    .addColumn('normalized_alias', 'text', (column) => column.notNull())
     .addColumn('is_primary', 'integer', (column) => column.notNull())
     .addColumn('created_at', 'text', (column) => column.notNull())
     .addColumn('updated_at', 'text', (column) => column.notNull())
+    .addUniqueConstraint('topic_aliases_space_normalized_alias_key', ['space_id', 'normalized_alias'])
+    .execute();
+
+  await db.schema
+    .createIndex('topics_space_id_idx')
+    .ifNotExists()
+    .on(TOPICS_TABLE)
+    .column('space_id')
+    .execute();
+
+  await db.schema
+    .createIndex('facts_space_id_idx')
+    .ifNotExists()
+    .on(FACTS_TABLE)
+    .column('space_id')
     .execute();
 
   await db.schema
@@ -133,6 +171,13 @@ export async function initializeSchema(
     .column('child_topic_id')
     .execute();
 
+  await db.schema
+    .createIndex('topic_aliases_space_id_idx')
+    .ifNotExists()
+    .on(TOPIC_ALIASES_TABLE)
+    .column('space_id')
+    .execute();
+
   await db.schema
     .createIndex('topic_aliases_topic_id_idx')
     .ifNotExists()
diff --git a/src/core/schema.ts b/src/core/schema.ts
index 5bbd72d..1dfa8f7 100644
--- a/src/core/schema.ts
+++ b/src/core/schema.ts
@@ -1,3 +1,4 @@
+export const SPACES_TABLE = 'spaces';
 export const TOPICS_TABLE = 'topics';
 export const FACTS_TABLE = 'facts';
 export const FACT_TOPICS_TABLE = 'fact_topics';
@@ -5,8 +6,19 @@ export const TOPIC_RELATIONS_TABLE = 'topic_relations';
 export const TOPIC_ALIASES_TABLE = 'topic_aliases';
 export const FACT_EMBEDDINGS_TABLE = 'fact_embeddings';
 
+export const SPACE_COLUMNS = [
+  'id',
+  'name',
+  'normalized_name',
+  'description',
+  'metadata',
+  'created_at',
+  'updated_at',
+] as const;
+
 export const TOPIC_COLUMNS = [
   'id',
+  'space_id',
   'name',
   'normalized_name',
   'category',
@@ -19,6 +31,7 @@ export const TOPIC_COLUMNS = [
 
 export const FACT_COLUMNS = [
   'id',
+  'space_id',
   'statement',
   'summary',
   'source',
@@ -45,6 +58,7 @@ export const TOPIC_RELATION_COLUMNS = [
 
 export const TOPIC_ALIAS_COLUMNS = [
   'id',
+  'space_id',
   'topic_id',
   'alias',
   'normalized_alias',
diff --git a/src/core/utils.ts b/src/core/utils.ts
index 5cbc795..d33cd72 100644
--- a/src/core/utils.ts
+++ b/src/core/utils.ts
@@ -1,7 +1,7 @@
 import { createHash, randomUUID } from 'node:crypto';
 
-import type { Fact, FactTopic, Topic } from '../types/api';
-import type { FactRecord, TopicRecord } from '../types/domain';
+import type { Fact, FactTopic, Space, Topic } from '../types/api';
+import type { FactRecord, SpaceRecord, TopicRecord } from '../types/domain';
 
 export function normalizeTopicName(name: string): string {
   return name.trim().replace(/\s+/g, ' ').toLowerCase();
@@ -11,6 +11,14 @@ export function canonicalizeTopicName(name: string): string {
   return name.trim().replace(/\s+/g, ' ');
 }
 
+export function normalizeSpaceName(name: string): string {
+  return normalizeTopicName(name);
+}
+
+export function canonicalizeSpaceName(name: string): string {
+  return canonicalizeTopicName(name);
+}
+
 export function nowIsoString(): string {
   return new Date().toISOString();
 }
@@ -71,9 +79,22 @@ export function cosineSimilarity(left: number[], right: number[]): number {
   return dot / (Math.sqrt(leftMagnitude) * Math.sqrt(rightMagnitude));
 }
 
+export function mapSpaceRow(record: SpaceRecord): Space {
+  return {
+    id: record.id,
+    name: record.name,
+    normalizedName: record.normalized_name,
+    description: record.description,
+    metadata: deserializeMetadata(record.metadata) as Space['metadata'],
+    createdAt: record.created_at,
+    updatedAt: record.updated_at,
+  };
+}
+
 export function mapTopicRow(record: TopicRecord): Topic {
   return {
     id: record.id,
+    spaceId: record.space_id,
     name: record.name,
     normalizedName: record.normalized_name,
     category: record.category,
@@ -88,6 +109,7 @@ export function mapTopicRow(record: TopicRecord): Topic {
 export function mapFactRow(record: FactRecord, topics: FactTopic[]): Fact {
   return {
     id: record.id,
+    spaceId: record.space_id,
     statement: record.statement,
     summary: record.summary,
     source: record.source,
diff --git a/src/ingestion/types.ts b/src/ingestion/types.ts
index 78327fc..50d82a4 100644
--- a/src/ingestion/types.ts
+++ b/src/ingestion/types.ts
@@ -31,4 +31,5 @@ export interface IngestStatementOptions {
   extractor: FactExtractor;
   embeddingProvider?: EmbeddingProvider;
   duplicateThreshold?: number;
+  spaceName?: string;
 }
diff --git a/src/queries/facts.ts b/src/queries/facts.ts
index d516b27..8e9ee33 100644
--- a/src/queries/facts.ts
+++ b/src/queries/facts.ts
@@ -13,12 +13,14 @@ export interface FactTopicJoinRow extends TopicRecord {
 
 export async function findFactRowsForTopicId(
   executor: DatabaseExecutor,
+  spaceId: string,
   topicId: string,
 ): Promise<FactRecord[]> {
   return executor
     .selectFrom('facts')
     .innerJoin('fact_topics', 'fact_topics.fact_id', 'facts.id')
     .selectAll('facts')
+    .where('facts.space_id', '=', spaceId)
     .where('fact_topics.topic_id', '=', topicId)
     .orderBy('facts.created_at', 'asc')
     .execute();
@@ -26,6 +28,7 @@ export async function findFactRowsForTopicId(
 
 export async function findFactRowsConnectingTopicIds(
   executor: DatabaseExecutor,
+  spaceId: string,
   topicIds: string[],
 ): Promise<FactRecord[]> {
   if (topicIds.length === 0) {
@@ -36,6 +39,7 @@ export async function findFactRowsConnectingTopicIds(
     .selectFrom('facts')
     .innerJoin('fact_topics', 'fact_topics.fact_id', 'facts.id')
     .selectAll('facts')
+    .where('facts.space_id', '=', spaceId)
     .where('fact_topics.topic_id', 'in', topicIds)
     .groupBy('facts.id')
     .having((eb) => eb.fn.count<number>('fact_topics.topic_id'), '=', topicIds.length)
@@ -45,6 +49,7 @@ export async function findFactRowsConnectingTopicIds(
 
 export async function findTopicLinksForFactIds(
   executor: DatabaseExecutor,
+  spaceId: string,
   factIds: string[],
 ): Promise<FactTopicJoinRow[]> {
   if (factIds.length === 0) {
@@ -60,6 +65,7 @@ export async function findTopicLinksForFactIds(
       'fact_topics.role as role',
       'fact_topics.position as position',
     ])
+    .where('topics.space_id', '=', spaceId)
     .where('fact_topics.fact_id', 'in', factIds)
     .orderBy('fact_topics.position', 'asc')
     .execute() as Promise<FactTopicJoinRow[]>;
diff --git a/src/queries/topics.ts b/src/queries/topics.ts
index d3c29de..2ade704 100644
--- a/src/queries/topics.ts
+++ b/src/queries/topics.ts
@@ -1,7 +1,7 @@
 import type { Kysely, Transaction } from 'kysely';
 
 import type { IdentityDatabaseSchema } from '../types/database';
-import type { TopicAliasRecord, TopicRecord } from '../types/domain';
+import type { SpaceRecord, TopicAliasRecord, TopicRecord } from '../types/domain';
 
 export type DatabaseExecutor = Kysely<IdentityDatabaseSchema> | Transaction<IdentityDatabaseSchema>;
 
@@ -9,48 +9,66 @@ export interface ConnectedTopicRow extends TopicRecord {
   shared_fact_count: number;
 }
 
+export async function findSpaceRowByNormalizedName(
+  executor: DatabaseExecutor,
+  normalizedName: string,
+): Promise<SpaceRecord | undefined> {
+  return executor
+    .selectFrom('spaces')
+    .selectAll()
+    .where('normalized_name', '=', normalizedName)
+    .executeTakeFirst();
+}
+
 export async function findTopicRowByNormalizedName(
   executor: DatabaseExecutor,
+  spaceId: string,
   normalizedName: string,
 ): Promise<TopicRecord | undefined> {
   return executor
     .selectFrom('topics')
     .selectAll()
+    .where('space_id', '=', spaceId)
     .where('normalized_name', '=', normalizedName)
     .executeTakeFirst();
 }
 
 export async function findTopicRowByNormalizedAlias(
   executor: DatabaseExecutor,
+  spaceId: string,
   normalizedAlias: string,
 ): Promise<TopicRecord | undefined> {
   return executor
     .selectFrom('topic_aliases')
     .innerJoin('topics', 'topics.id', 'topic_aliases.topic_id')
     .selectAll('topics')
+    .where('topic_aliases.space_id', '=', spaceId)
     .where('topic_aliases.normalized_alias', '=', normalizedAlias)
     .executeTakeFirst();
 }
 
 export async function findTopicRowByNameOrAlias(
   executor: DatabaseExecutor,
+  spaceId: string,
   normalizedName: string,
 ): Promise<TopicRecord | undefined> {
-  const directMatch = await findTopicRowByNormalizedName(executor, normalizedName);
+  const directMatch = await findTopicRowByNormalizedName(executor, spaceId, normalizedName);
   if (directMatch) {
     return directMatch;
   }
 
-  return findTopicRowByNormalizedAlias(executor, normalizedName);
+  return findTopicRowByNormalizedAlias(executor, spaceId, normalizedName);
 }
 
 export async function listTopicAliasRowsForTopicId(
   executor: DatabaseExecutor,
+  spaceId: string,
   topicId: string,
 ): Promise<TopicAliasRecord[]> {
   return executor
     .selectFrom('topic_aliases')
     .selectAll()
+    .where('space_id', '=', spaceId)
     .where('topic_id', '=', topicId)
     .orderBy('is_primary', 'desc')
     .orderBy('normalized_alias', 'asc')
@@ -59,9 +77,14 @@ export async function listTopicAliasRowsForTopicId(
 
 export async function listTopicRows(
   executor: DatabaseExecutor,
+  spaceId: string,
   limit?: number,
 ): Promise<TopicRecord[]> {
-  let query = executor.selectFrom('topics').selectAll().orderBy('normalized_name', 'asc');
+  let query = executor
+    .selectFrom('topics')
+    .selectAll()
+    .where('space_id', '=', spaceId)
+    .orderBy('normalized_name', 'asc');
 
   if (limit !== undefined) {
     query = query.limit(limit);
@@ -72,14 +95,18 @@ export async function listTopicRows(
 
 export async function findConnectedTopicRows(
   executor: DatabaseExecutor,
+  spaceId: string,
   topicId: string,
 ): Promise<ConnectedTopicRow[]> {
   return executor
     .selectFrom('fact_topics as source_link')
+    .innerJoin('facts', 'facts.id', 'source_link.fact_id')
     .innerJoin('fact_topics as related_link', 'related_link.fact_id', 'source_link.fact_id')
     .innerJoin('topics', 'topics.id', 'related_link.topic_id')
     .selectAll('topics')
     .select((eb) => eb.fn.count<number>('related_link.fact_id').as('shared_fact_count'))
+    .where('facts.space_id', '=', spaceId)
+    .where('topics.space_id', '=', spaceId)
     .where('source_link.topic_id', '=', topicId)
     .whereRef('related_link.topic_id', '!=', 'source_link.topic_id')
     .groupBy('topics.id')
@@ -90,12 +117,14 @@ export async function findConnectedTopicRows(
 
 export async function findChildTopicRows(
   executor: DatabaseExecutor,
+  spaceId: string,
   parentTopicId: string,
 ): Promise<TopicRecord[]> {
   return executor
     .selectFrom('topic_relations')
     .innerJoin('topics', 'topics.id', 'topic_relations.child_topic_id')
     .selectAll('topics')
+    .where('topics.space_id', '=', spaceId)
     .where('topic_relations.parent_topic_id', '=', parentTopicId)
     .where('topic_relations.relation', '=', 'parent_of')
     .orderBy('topics.normalized_name', 'asc')
@@ -104,12 +133,14 @@ export async function findChildTopicRows(
 
 export async function findParentTopicRows(
   executor: DatabaseExecutor,
+  spaceId: string,
   childTopicId: string,
 ): Promise<TopicRecord[]> {
   return executor
     .selectFrom('topic_relations')
     .innerJoin('topics', 'topics.id', 'topic_relations.parent_topic_id')
     .selectAll('topics')
+    .where('topics.space_id', '=', spaceId)
     .where('topic_relations.child_topic_id', '=', childTopicId)
     .where('topic_relations.relation', '=', 'parent_of')
     .orderBy('topics.normalized_name', 'asc')
diff --git a/src/types/api.ts b/src/types/api.ts
index 20cee77..5257f65 100644
--- a/src/types/api.ts
+++ b/src/types/api.ts
@@ -1,6 +1,26 @@
 import type { JsonValue, TopicCategory, TopicGranularity } from './domain';
 
-export interface UpsertTopicInput {
+export interface SpaceScopedInput {
+  spaceName?: string | undefined;
+}
+
+export interface UpsertSpaceInput {
+  name: string;
+  description?: string | null;
+  metadata?: JsonValue | null;
+}
+
+export interface Space {
+  id: string;
+  name: string;
+  normalizedName: string;
+  description: string | null;
+  metadata: JsonValue | null;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface UpsertTopicInput extends SpaceScopedInput {
   name: string;
   category?: TopicCategory;
   granularity?: TopicGranularity;
@@ -12,7 +32,7 @@ export interface TopicLinkInput extends UpsertTopicInput {
   role?: string | null;
 }
 
-export interface AddFactInput {
+export interface AddFactInput extends SpaceScopedInput {
   statement: string;
   summary?: string | null;
   source?: string | null;
@@ -21,13 +41,14 @@ export interface AddFactInput {
   topics: TopicLinkInput[];
 }
 
-export interface LinkTopicsInput {
+export interface LinkTopicsInput extends SpaceScopedInput {
   parentName: string;
   childName: string;
 }
 
 export interface Topic {
   id: string;
+  spaceId: string;
   name: string;
   normalizedName: string;
   category: TopicCategory;
@@ -45,6 +66,7 @@ export interface FactTopic extends Topic {
 
 export interface Fact {
   id: string;
+  spaceId: string;
   statement: string;
   summary: string | null;
   source: string | null;
@@ -63,11 +85,11 @@ export interface ConnectedTopic extends Topic {
   sharedFactCount: number;
 }
 
-export interface TopicLookupOptions {
+export interface TopicLookupOptions extends SpaceScopedInput {
   includeFacts?: boolean;
 }
 
-export interface ListTopicsOptions {
+export interface ListTopicsOptions extends SpaceScopedInput {
   includeFacts?: boolean;
   limit?: number;
 }
@@ -79,11 +101,11 @@ export interface EmbeddingProvider {
   embedMany?(inputs: string[]): Promise<number[][]>;
 }
 
-export interface IndexFactEmbeddingsInput {
+export interface IndexFactEmbeddingsInput extends SpaceScopedInput {
   provider: EmbeddingProvider;
 }
 
-export interface SearchFactsInput {
+export interface SearchFactsInput extends SpaceScopedInput {
   query: string;
   provider: EmbeddingProvider;
   topicNames?: string[];
@@ -91,7 +113,7 @@ export interface SearchFactsInput {
   minimumScore?: number;
 }
 
-export interface FindSimilarFactsInput {
+export interface FindSimilarFactsInput extends SpaceScopedInput {
   statement: string;
   provider: EmbeddingProvider;
   topicNames?: string[];
diff --git a/src/types/database.ts b/src/types/database.ts
index 8c9e8ae..f845484 100644
--- a/src/types/database.ts
+++ b/src/types/database.ts
@@ -2,12 +2,14 @@ import type {
   FactEmbeddingRecord,
   FactRecord,
   FactTopicRecord,
+  SpaceRecord,
   TopicAliasRecord,
   TopicRecord,
   TopicRelationRecord,
 } from './domain';
 
 export interface IdentityDatabaseSchema {
+  spaces: SpaceRecord;
   topics: TopicRecord;
   facts: FactRecord;
   fact_topics: FactTopicRecord;
diff --git a/src/types/domain.ts b/src/types/domain.ts
index ad94f4b..3d90d40 100644
--- a/src/types/domain.ts
+++ b/src/types/domain.ts
@@ -5,8 +5,19 @@ export type TopicGranularity = 'abstract' | 'concrete' | 'mixed';
 export type JsonPrimitive = string | number | boolean | null;
 export type JsonValue = JsonPrimitive | JsonValue[] | { [key: string]: JsonValue };
 
+export interface SpaceRecord {
+  id: string;
+  name: string;
+  normalized_name: string;
+  description: string | null;
+  metadata: string | null;
+  created_at: string;
+  updated_at: string;
+}
+
 export interface TopicRecord {
   id: string;
+  space_id: string;
   name: string;
   normalized_name: string;
   category: TopicCategory;
@@ -19,6 +30,7 @@ export interface TopicRecord {
 
 export interface FactRecord {
   id: string;
+  space_id: string;
   statement: string;
   summary: string | null;
   source: string | null;
@@ -45,6 +57,7 @@ export interface TopicRelationRecord {
 
 export interface TopicAliasRecord {
   id: string;
+  space_id: string;
   topic_id: string;
   alias: string;
   normalized_alias: string;
diff --git a/tests/identity-db.test.ts b/tests/identity-db.test.ts
index 8f37872..302b6c4 100644
--- a/tests/identity-db.test.ts
+++ b/tests/identity-db.test.ts
@@ -34,6 +34,58 @@ describe('IdentityDB topic and fact writes', () => {
     expect(topics).toHaveLength(1);
   });
 
+  it('keeps same normalized topic names isolated across spaces', async () => {
+    const alpha = await db.upsertTopic({
+      name: 'TypeScript',
+      category: 'entity',
+      granularity: 'concrete',
+      spaceName: 'A',
+    });
+
+    const beta = await db.upsertTopic({
+      name: 'TypeScript',
+      category: 'entity',
+      granularity: 'concrete',
+      spaceName: 'B',
+    });
+
+    expect(beta.id).not.toBe(alpha.id);
+
+    const alphaTopics = await db.listTopics({ includeFacts: false, spaceName: 'A' });
+    const betaTopics = await db.listTopics({ includeFacts: false, spaceName: 'B' });
+    const defaultTopics = await db.listTopics({ includeFacts: false });
+
+    expect(alphaTopics.map((topic) => topic.name)).toEqual(['TypeScript']);
+    expect(betaTopics.map((topic) => topic.name)).toEqual(['TypeScript']);
+    expect(defaultTopics).toHaveLength(0);
+  });
+
+  it('keeps alias resolution scoped to the requested space', async () => {
+    await db.upsertTopic({
+      name: 'TypeScript',
+      category: 'entity',
+      granularity: 'concrete',
+      spaceName: 'A',
+    });
+    await db.upsertTopic({
+      name: 'TeamSpeak',
+      category: 'entity',
+      granularity: 'concrete',
+      spaceName: 'B',
+    });
+
+    await db.addTopicAlias('TypeScript', 'TS', { spaceName: 'A' });
+    await db.addTopicAlias('TeamSpeak', 'TS', { spaceName: 'B' });
+
+    const alphaResolved = await db.resolveTopic('ts', { spaceName: 'A' });
+    const betaResolved = await db.resolveTopic('ts', { spaceName: 'B' });
+    const defaultResolved = await db.resolveTopic('ts');
+
+    expect(alphaResolved?.name).toBe('TypeScript');
+    expect(betaResolved?.name).toBe('TeamSpeak');
+    expect(defaultResolved).toBeNull();
+  });
+
   it('adds one fact that links multiple topics', async () => {
     const fact = await db.addFact({
       statement: 'I have worked with TypeScript since 2025.',
diff --git a/tests/migrations.test.ts b/tests/migrations.test.ts
index 20b072e..d12042e 100644
--- a/tests/migrations.test.ts
+++ b/tests/migrations.test.ts
@@ -16,7 +16,7 @@ afterEach(async () => {
 });
 
 describe('initializeSchema', () => {
-  it('creates the topics, facts, fact_embeddings, fact_topics, topic_relations, and topic_aliases tables', async () => {
+  it('creates the spaces, topics, facts, fact_embeddings, fact_topics, topic_relations, and topic_aliases tables', async () => {
     const connection = await createDatabase({ client: 'sqlite', filename: ':memory:' });
     openConnections.push(connection.destroy);
 
@@ -31,6 +31,7 @@ describe('initializeSchema', () => {
 
     const tableNames = tables.rows.map((row) => row.name);
 
+    expect(tableNames).toContain('spaces');
     expect(tableNames).toContain('topics');
     expect(tableNames).toContain('facts');
     expect(tableNames).toContain('fact_embeddings');
@@ -45,6 +46,7 @@ describe('initializeSchema', () => {
 
     await initializeSchema(connection.db);
 
+    const spaceColumns = await sql<{ name: string }>`PRAGMA table_info(spaces)`.execute(connection.db);
     const topicsColumns = await sql<{ name: string }>`PRAGMA table_info(topics)`.execute(connection.db);
     const factsColumns = await sql<{ name: string }>`PRAGMA table_info(facts)`.execute(connection.db);
     const factEmbeddingsColumns = await sql<{ name: string }>`PRAGMA table_info(fact_embeddings)`.execute(connection.db);
@@ -52,8 +54,19 @@ describe('initializeSchema', () => {
     const topicRelationsColumns = await sql<{ name: string }>`PRAGMA table_info(topic_relations)`.execute(connection.db);
     const topicAliasesColumns = await sql<{ name: string }>`PRAGMA table_info(topic_aliases)`.execute(connection.db);
 
+    expect(spaceColumns.rows.map((row) => row.name)).toEqual([
+      'id',
+      'name',
+      'normalized_name',
+      'description',
+      'metadata',
+      'created_at',
+      'updated_at',
+    ]);
+
     expect(topicsColumns.rows.map((row) => row.name)).toEqual([
       'id',
+      'space_id',
       'name',
       'normalized_name',
       'category',
@@ -66,6 +79,7 @@ describe('initializeSchema', () => {
 
     expect(factsColumns.rows.map((row) => row.name)).toEqual([
       'id',
+      'space_id',
       'statement',
       'summary',
       'source',
@@ -102,6 +116,7 @@ describe('initializeSchema', () => {
 
     expect(topicAliasesColumns.rows.map((row) => row.name)).toEqual([
       'id',
+      'space_id',
       'topic_id',
       'alias',
       'normalized_alias',
diff --git a/tests/queries.test.ts b/tests/queries.test.ts
index 25dbcbd..f32cd4b 100644
--- a/tests/queries.test.ts
+++ b/tests/queries.test.ts
@@ -2,9 +2,10 @@ import { afterEach, beforeEach, describe, expect, it } from 'vitest';
 
 import { IdentityDB } from '../src/core/identity-db';
 
-async function seedMemoryGraph(db: IdentityDB): Promise<void> {
+async function seedMemoryGraph(db: IdentityDB, spaceName?: string): Promise<void> {
   await db.addFact({
     statement: 'I have worked with TypeScript since 2025.',
+    spaceName,
     topics: [
       { name: 'I', category: 'entity', granularity: 'concrete', role: 'subject' },
       { name: 'TypeScript', category: 'entity', granularity: 'concrete', role: 'object' },
@@ -14,6 +15,7 @@ async function seedMemoryGraph(db: IdentityDB): Promise<void> {
 
   await db.addFact({
     statement: 'TypeScript is a programming language.',
+    spaceName,
     topics: [
       { name: 'TypeScript', category: 'entity', granularity: 'concrete', role: 'subject' },
       { name: 'programming language', category: 'concept', granularity: 'abstract', role: 'classification' },
@@ -23,11 +25,13 @@ async function seedMemoryGraph(db: IdentityDB): Promise<void> {
   await db.linkTopics({
     parentName: 'software technology',
     childName: 'programming language',
+    spaceName,
   });
 
   await db.linkTopics({
     parentName: 'programming language',
     childName: 'TypeScript',
+    spaceName,
   });
 }
 
@@ -114,6 +118,56 @@ describe('IdentityDB queries', () => {
     ]);
   });
 
+  it('keeps hierarchy and fact queries isolated per space', async () => {
+    const isolatedDb = await IdentityDB.connect({ client: 'sqlite', filename: ':memory:' });
+    try {
+      await isolatedDb.initialize();
+      await seedMemoryGraph(isolatedDb, 'A');
+
+      await isolatedDb.addFact({
+        statement: 'TypeScript is a typed superset.',
+        spaceName: 'B',
+        topics: [
+          { name: 'TypeScript', category: 'entity', granularity: 'concrete', role: 'subject' },
+          { name: 'superset', category: 'concept', granularity: 'abstract', role: 'classification' },
+        ],
+      });
+
+      await isolatedDb.linkTopics({
+        parentName: 'language family',
+        childName: 'TypeScript',
+        spaceName: 'B',
+      });
+
+      const alphaTopic = await isolatedDb.getTopicByName('TypeScript', {
+        includeFacts: true,
+        spaceName: 'A',
+      });
+      const betaTopic = await isolatedDb.getTopicByName('TypeScript', {
+        includeFacts: true,
+        spaceName: 'B',
+      });
+      const alphaParents = await isolatedDb.getTopicParents('TypeScript', { spaceName: 'A' });
+      const betaParents = await isolatedDb.getTopicParents('TypeScript', { spaceName: 'B' });
+      const alphaConnected = await isolatedDb.findConnectedTopics('TypeScript', { spaceName: 'A' });
+      const betaConnected = await isolatedDb.findConnectedTopics('TypeScript', { spaceName: 'B' });
+
+      expect(alphaTopic?.facts.map((fact) => fact.statement)).toEqual([
+        'I have worked with TypeScript since 2025.',
+        'TypeScript is a programming language.',
+      ]);
+      expect(betaTopic?.facts.map((fact) => fact.statement)).toEqual([
+        'TypeScript is a typed superset.',
+      ]);
+      expect(alphaParents.map((topic) => topic.name)).toEqual(['programming language']);
+      expect(betaParents.map((topic) => topic.name)).toEqual(['language family']);
+      expect(alphaConnected.map((topic) => topic.name)).toEqual(['2025', 'I', 'programming language']);
+      expect(betaConnected.map((topic) => topic.name)).toEqual(['superset']);
+    } finally {
+      await isolatedDb.close();
+    }
+  });
+
   it('resolves alias names in topic lookups', async () => {
     await db.addTopicAlias('TypeScript', 'TS');
 
diff --git a/tests/semantic-search.test.ts b/tests/semantic-search.test.ts
index 131324d..a51b8e6 100644
--- a/tests/semantic-search.test.ts
+++ b/tests/semantic-search.test.ts
@@ -120,6 +120,53 @@ describe('IdentityDB semantic search', () => {
     expect(matches[0]?.statement).toBe('Bun runs TypeScript tooling quickly.');
     expect(matches[0]!.score).toBeGreaterThan(matches[1]!.score);
   });
+
+  it('keeps semantic search isolated per space', async () => {
+    const isolatedDb = await IdentityDB.connect({ client: 'sqlite', filename: ':memory:' });
+    try {
+      await isolatedDb.initialize();
+
+      await isolatedDb.addFact({
+        statement: 'Bun runs TypeScript tooling quickly.',
+        spaceName: 'A',
+        topics: [
+          { name: 'Bun', category: 'entity', granularity: 'concrete' },
+          { name: 'TypeScript', category: 'entity', granularity: 'concrete' },
+        ],
+      });
+
+      await isolatedDb.addFact({
+        statement: 'TypeScript runtime tooling belongs to another tenant.',
+        spaceName: 'B',
+        topics: [
+          { name: 'TypeScript', category: 'entity', granularity: 'concrete' },
+        ],
+      });
+
+      await isolatedDb.indexFactEmbeddings({ provider, spaceName: 'A' });
+      await isolatedDb.indexFactEmbeddings({ provider, spaceName: 'B' });
+
+      const alphaMatches = await isolatedDb.searchFacts({
+        query: 'TypeScript runtime tooling',
+        provider,
+        spaceName: 'A',
+      });
+      const betaMatches = await isolatedDb.searchFacts({
+        query: 'TypeScript runtime tooling',
+        provider,
+        spaceName: 'B',
+      });
+
+      expect(alphaMatches.map((match) => match.statement)).toEqual([
+        'Bun runs TypeScript tooling quickly.',
+      ]);
+      expect(betaMatches.map((match) => match.statement)).toEqual([
+        'TypeScript runtime tooling belongs to another tenant.',
+      ]);
+    } finally {
+      await isolatedDb.close();
+    }
+  });
 });
 
 describe('IdentityDB dedup-aware ingestion', () => {
@@ -167,4 +214,26 @@ describe('IdentityDB dedup-aware ingestion', () => {
     expect(facts).toHaveLength(1);
     expect(facts[0]?.statement).toBe('Bun runs TypeScript tooling quickly.');
   });
+
+  it('does not reuse a semantic duplicate from another space', async () => {
+    const first = await db.ingestStatement('Bun runs TypeScript tooling quickly.', {
+      extractor,
+      embeddingProvider: provider,
+      spaceName: 'A',
+    });
+
+    const second = await db.ingestStatement('Bun makes TypeScript tooling fast.', {
+      extractor,
+      embeddingProvider: provider,
+      duplicateThreshold: 0.95,
+      spaceName: 'B',
+    });
+
+    const alphaFacts = await db.getTopicFacts('TypeScript', { spaceName: 'A' });
+    const betaFacts = await db.getTopicFacts('TypeScript', { spaceName: 'B' });
+
+    expect(second.id).not.toBe(first.id);
+    expect(alphaFacts).toHaveLength(1);
+    expect(betaFacts).toHaveLength(1);
+  });
 });