diff --git a/src/core/identity-db.ts b/src/core/identity-db.ts
new file mode 100644
index 0000000..560ee54
--- /dev/null
+++ b/src/core/identity-db.ts
@@ -0,0 +1,298 @@
+import {
+  type ConnectedTopic,
+  type Fact,
+  type FactTopic,
+  type ListTopicsOptions,
+  type Topic,
+  type TopicLookupOptions,
+  type TopicWithFacts,
+  type UpsertTopicInput,
+  type AddFactInput,
+} from '../types/api';
+import type { DatabaseConnection, IdentityDBConnectionConfig } from '../adapters/dialect';
+import type { IdentityDatabaseSchema } from '../types/database';
+import type { FactRecord, TopicRecord } from '../types/domain';
+import { createDatabase } from '../adapters/dialect';
+import { IdentityDBError } from './errors';
+import { initializeSchema } from './migrations';
+import {
+  canonicalizeTopicName,
+  createId,
+  mapFactRow,
+  mapTopicRow,
+  normalizeTopicName,
+  nowIsoString,
+  serializeMetadata,
+} from './utils';
+import {
+  findFactRowsConnectingTopicIds,
+  findFactRowsForTopicId,
+  findTopicLinksForFactIds,
+} from '../queries/facts';
+import {
+  findConnectedTopicRows,
+  findTopicRowByNormalizedName,
+  listTopicRows,
+  type DatabaseExecutor,
+} from '../queries/topics';
+
+export class IdentityDB {
+  private constructor(private readonly connection: DatabaseConnection) {}
+
+  static async connect(config: IdentityDBConnectionConfig): Promise<IdentityDB> {
+    const connection = await createDatabase(config);
+    return new IdentityDB(connection);
+  }
+
+  async initialize(): Promise<void> {
+    await initializeSchema(this.connection.db);
+  }
+
+  async close(): Promise<void> {
+    await this.connection.destroy();
+  }
+
+  async upsertTopic(input: UpsertTopicInput): Promise<Topic> {
+    return this.upsertTopicInExecutor(this.connection.db, input);
+  }
+
+  async addFact(input: AddFactInput): Promise<Fact> {
+    if (input.statement.trim().length === 0) {
+      throw new IdentityDBError('Fact statement cannot be empty.');
+    }
+
+    if (input.topics.length === 0) {
+      throw new IdentityDBError('A fact must be linked to at least one topic.');
+    }
+
+    return this.connection.db.transaction().execute(async (trx) => {
+      const createdAt = nowIsoString();
+      const factId = createId();
+
+      await trx
+        .insertInto('facts')
+        .values({
+          id: factId,
+          statement: input.statement.trim(),
+          summary: input.summary ?? null,
+          source: input.source ?? null,
+          confidence: input.confidence ?? null,
+          metadata: serializeMetadata(input.metadata),
+          created_at: createdAt,
+          updated_at: createdAt,
+        })
+        .execute();
+
+      const topics: FactTopic[] = [];
+
+      for (const [index, topicInput] of input.topics.entries()) {
+        const topic = await this.upsertTopicInExecutor(trx, topicInput);
+
+        await trx
+          .insertInto('fact_topics')
+          .values({
+            fact_id: factId,
+            topic_id: topic.id,
+            role: topicInput.role ?? null,
+            position: index,
+            created_at: createdAt,
+          })
+          .execute();
+
+        topics.push({
+          ...topic,
+          role: topicInput.role ?? null,
+          position: index,
+        });
+      }
+
+      return {
+        id: factId,
+        statement: input.statement.trim(),
+        summary: input.summary ?? null,
+        source: input.source ?? null,
+        confidence: input.confidence ?? null,
+        metadata: input.metadata ?? null,
+        createdAt,
+        updatedAt: createdAt,
+        topics,
+      };
+    });
+  }
+
+  async getTopicFacts(name: string): Promise<Fact[]> {
+    const topicRow = await this.getRequiredTopicRow(name);
+
+    if (!topicRow) {
+      return [];
+    }
+
+    const factRows = await findFactRowsForTopicId(this.connection.db, topicRow.id);
+    return this.hydrateFacts(factRows);
+  }
+
+  async getTopicFactsLinkedTo(name: string, linkedTopicName: string): Promise<Fact[]> {
+    return this.findFactsConnectingTopics([name, linkedTopicName]);
+  }
+
+  async findFactsConnectingTopics(names: string[]): Promise<Fact[]> {
+    if (names.length === 0) {
+      return [];
+    }
+
+    const topicRows = await Promise.all(names.map((name) => this.getRequiredTopicRow(name)));
+
+    if (topicRows.some((topicRow) => topicRow === undefined)) {
+      return [];
+    }
+
+    const topicIds = topicRows.map((topicRow) => topicRow!.id);
+    const factRows = await findFactRowsConnectingTopicIds(this.connection.db, topicIds);
+
+    return this.hydrateFacts(factRows);
+  }
+
+  async getTopicByName(
+    name: string,
+    options: { includeFacts: true },
+  ): 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);
+
+    if (!topicRow) {
+      return null;
+    }
+
+    const topic = mapTopicRow(topicRow);
+
+    if (options?.includeFacts) {
+      return {
+        ...topic,
+        facts: await this.getTopicFacts(name),
+      };
+    }
+
+    return topic;
+  }
+
+  async listTopics(options: { includeFacts: true; limit?: number }): Promise<TopicWithFacts[]>;
+  async listTopics(options?: ListTopicsOptions): Promise<Topic[]>;
+  async listTopics(
+    options?: ListTopicsOptions,
+  ): Promise<Topic[] | TopicWithFacts[]> {
+    const rows = await listTopicRows(this.connection.db, 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),
+      });
+    }
+
+    return topicsWithFacts;
+  }
+
+  async findConnectedTopics(name: string): Promise<ConnectedTopic[]> {
+    const topicRow = await this.getRequiredTopicRow(name);
+
+    if (!topicRow) {
+      return [];
+    }
+
+    const rows = await findConnectedTopicRows(this.connection.db, topicRow.id);
+
+    return rows.map((row) => ({
+      ...mapTopicRow(row),
+      sharedFactCount: row.shared_fact_count,
+    }));
+  }
+
+  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 now = nowIsoString();
+
+    if (existing) {
+      await executor
+        .updateTable('topics')
+        .set({
+          name: canonicalizeTopicName(input.name),
+          category: input.category ?? existing.category,
+          granularity: input.granularity ?? existing.granularity,
+          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 executor
+        .selectFrom('topics')
+        .selectAll()
+        .where('id', '=', existing.id)
+        .executeTakeFirstOrThrow();
+
+      return mapTopicRow(updated);
+    }
+
+    const createdRow: TopicRecord = {
+      id: createId(),
+      name: canonicalizeTopicName(input.name),
+      normalized_name: normalizedName,
+      category: input.category ?? 'custom',
+      granularity: input.granularity ?? 'mixed',
+      description: input.description ?? null,
+      metadata: serializeMetadata(input.metadata),
+      created_at: now,
+      updated_at: now,
+    };
+
+    await executor.insertInto('topics').values(createdRow).execute();
+
+    return mapTopicRow(createdRow);
+  }
+
+  private async getRequiredTopicRow(name: string): Promise<TopicRecord | undefined> {
+    return findTopicRowByNormalizedName(this.connection.db, normalizeTopicName(name));
+  }
+
+  private async hydrateFacts(factRows: FactRecord[]): Promise<Fact[]> {
+    const factIds = factRows.map((fact) => fact.id);
+    const topicLinks = await findTopicLinksForFactIds(this.connection.db, factIds);
+
+    const topicsByFactId = new Map<string, FactTopic[]>();
+
+    for (const topicLink of topicLinks) {
+      const topics = topicsByFactId.get(topicLink.fact_id) ?? [];
+      topics.push({
+        ...mapTopicRow(topicLink),
+        role: topicLink.role,
+        position: topicLink.position,
+      });
+      topicsByFactId.set(topicLink.fact_id, topics);
+    }
+
+    return factRows.map((factRow) => mapFactRow(factRow, topicsByFactId.get(factRow.id) ?? []));
+  }
+}
diff --git a/src/core/utils.ts b/src/core/utils.ts
new file mode 100644
index 0000000..022f139
--- /dev/null
+++ b/src/core/utils.ts
@@ -0,0 +1,64 @@
+import { randomUUID } from 'node:crypto';
+
+import type { Fact, FactTopic, Topic } from '../types/api';
+import type { FactRecord, TopicRecord } from '../types/domain';
+
+export function normalizeTopicName(name: string): string {
+  return name.trim().replace(/\s+/g, ' ').toLowerCase();
+}
+
+export function canonicalizeTopicName(name: string): string {
+  return name.trim().replace(/\s+/g, ' ');
+}
+
+export function nowIsoString(): string {
+  return new Date().toISOString();
+}
+
+export function createId(): string {
+  return randomUUID();
+}
+
+export function serializeMetadata(metadata: unknown): string | null {
+  if (metadata === undefined || metadata === null) {
+    return null;
+  }
+
+  return JSON.stringify(metadata);
+}
+
+export function deserializeMetadata(metadata: string | null): unknown | null {
+  if (metadata === null) {
+    return null;
+  }
+
+  return JSON.parse(metadata);
+}
+
+export function mapTopicRow(record: TopicRecord): Topic {
+  return {
+    id: record.id,
+    name: record.name,
+    normalizedName: record.normalized_name,
+    category: record.category,
+    granularity: record.granularity,
+    description: record.description,
+    metadata: deserializeMetadata(record.metadata) as Topic['metadata'],
+    createdAt: record.created_at,
+    updatedAt: record.updated_at,
+  };
+}
+
+export function mapFactRow(record: FactRecord, topics: FactTopic[]): Fact {
+  return {
+    id: record.id,
+    statement: record.statement,
+    summary: record.summary,
+    source: record.source,
+    confidence: record.confidence,
+    metadata: deserializeMetadata(record.metadata) as Fact['metadata'],
+    createdAt: record.created_at,
+    updatedAt: record.updated_at,
+    topics,
+  };
+}
diff --git a/src/index.ts b/src/index.ts
index cb0ff5c..86f9b1b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1,6 @@
-export {};
+export * from './adapters';
+export * from './core/identity-db';
+export * from './core/migrations';
+export * from './types/api';
+export * from './types/database';
+export * from './types/domain';
diff --git a/src/queries/facts.ts b/src/queries/facts.ts
new file mode 100644
index 0000000..d516b27
--- /dev/null
+++ b/src/queries/facts.ts
@@ -0,0 +1,66 @@
+import type { Kysely, Transaction } from 'kysely';
+
+import type { IdentityDatabaseSchema } from '../types/database';
+import type { FactRecord, TopicRecord } from '../types/domain';
+
+export type DatabaseExecutor = Kysely<IdentityDatabaseSchema> | Transaction<IdentityDatabaseSchema>;
+
+export interface FactTopicJoinRow extends TopicRecord {
+  fact_id: string;
+  role: string | null;
+  position: number;
+}
+
+export async function findFactRowsForTopicId(
+  executor: DatabaseExecutor,
+  topicId: string,
+): Promise<FactRecord[]> {
+  return executor
+    .selectFrom('facts')
+    .innerJoin('fact_topics', 'fact_topics.fact_id', 'facts.id')
+    .selectAll('facts')
+    .where('fact_topics.topic_id', '=', topicId)
+    .orderBy('facts.created_at', 'asc')
+    .execute();
+}
+
+export async function findFactRowsConnectingTopicIds(
+  executor: DatabaseExecutor,
+  topicIds: string[],
+): Promise<FactRecord[]> {
+  if (topicIds.length === 0) {
+    return [];
+  }
+
+  return executor
+    .selectFrom('facts')
+    .innerJoin('fact_topics', 'fact_topics.fact_id', 'facts.id')
+    .selectAll('facts')
+    .where('fact_topics.topic_id', 'in', topicIds)
+    .groupBy('facts.id')
+    .having((eb) => eb.fn.count<number>('fact_topics.topic_id'), '=', topicIds.length)
+    .orderBy('facts.created_at', 'asc')
+    .execute();
+}
+
+export async function findTopicLinksForFactIds(
+  executor: DatabaseExecutor,
+  factIds: string[],
+): Promise<FactTopicJoinRow[]> {
+  if (factIds.length === 0) {
+    return [];
+  }
+
+  return executor
+    .selectFrom('fact_topics')
+    .innerJoin('topics', 'topics.id', 'fact_topics.topic_id')
+    .selectAll('topics')
+    .select([
+      'fact_topics.fact_id as fact_id',
+      'fact_topics.role as role',
+      'fact_topics.position as position',
+    ])
+    .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
new file mode 100644
index 0000000..fb71093
--- /dev/null
+++ b/src/queries/topics.ts
@@ -0,0 +1,55 @@
+import type { Kysely, Transaction } from 'kysely';
+
+import type { IdentityDatabaseSchema } from '../types/database';
+import type { TopicRecord } from '../types/domain';
+
+export type DatabaseExecutor = Kysely<IdentityDatabaseSchema> | Transaction<IdentityDatabaseSchema>;
+
+export interface ConnectedTopicRow extends TopicRecord {
+  shared_fact_count: number;
+}
+
+export async function findTopicRowByNormalizedName(
+  executor: DatabaseExecutor,
+  normalizedName: string,
+): Promise<TopicRecord | undefined> {
+  return executor
+    .selectFrom('topics')
+    .selectAll()
+    .where('normalized_name', '=', normalizedName)
+    .executeTakeFirst();
+}
+
+export async function listTopicRows(
+  executor: DatabaseExecutor,
+  limit?: number,
+): Promise<TopicRecord[]> {
+  let query = executor
+    .selectFrom('topics')
+    .selectAll()
+    .orderBy('normalized_name', 'asc');
+
+  if (limit !== undefined) {
+    query = query.limit(limit);
+  }
+
+  return query.execute();
+}
+
+export async function findConnectedTopicRows(
+  executor: DatabaseExecutor,
+  topicId: string,
+): Promise<ConnectedTopicRow[]> {
+  return executor
+    .selectFrom('fact_topics as source_link')
+    .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('source_link.topic_id', '=', topicId)
+    .whereRef('related_link.topic_id', '!=', 'source_link.topic_id')
+    .groupBy('topics.id')
+    .orderBy('shared_fact_count', 'desc')
+    .orderBy('topics.normalized_name', 'asc')
+    .execute() as Promise<ConnectedTopicRow[]>;
+}
diff --git a/src/types/api.ts b/src/types/api.ts
index 06ea540..10c1346 100644
--- a/src/types/api.ts
+++ b/src/types/api.ts
@@ -20,3 +20,49 @@ export interface AddFactInput {
   metadata?: JsonValue | null;
   topics: TopicLinkInput[];
 }
+
+export interface Topic {
+  id: string;
+  name: string;
+  normalizedName: string;
+  category: TopicCategory;
+  granularity: TopicGranularity;
+  description: string | null;
+  metadata: JsonValue | null;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface FactTopic extends Topic {
+  role: string | null;
+  position: number;
+}
+
+export interface Fact {
+  id: string;
+  statement: string;
+  summary: string | null;
+  source: string | null;
+  confidence: number | null;
+  metadata: JsonValue | null;
+  createdAt: string;
+  updatedAt: string;
+  topics: FactTopic[];
+}
+
+export interface TopicWithFacts extends Topic {
+  facts: Fact[];
+}
+
+export interface ConnectedTopic extends Topic {
+  sharedFactCount: number;
+}
+
+export interface TopicLookupOptions {
+  includeFacts?: boolean;
+}
+
+export interface ListTopicsOptions {
+  includeFacts?: boolean;
+  limit?: number;
+}