diff --git a/packages/auth/src/di/container.test.ts b/packages/auth/src/di/container.test.ts
new file mode 100644
index 0000000..73399e3
--- /dev/null
+++ b/packages/auth/src/di/container.test.ts
@@ -0,0 +1,51 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { authContainer } from "./container";
+import { AUTH_SYMBOLS } from "./symbols";
+import { AuthModule } from "./module";
+import { MockUsersRepository } from "@/infrastructure/repositories/mock-users.repository";
+import { MockAuthenticationService } from "@/infrastructure/services/mock-authentication.service";
+import type { IUsersRepository } from "@/application/repositories/users-repository.interface";
+import type { IAuthenticationService } from "@/application/services/authentication-service.interface";
+
+describe("authContainer", () => {
+  beforeEach(() => {
+    authContainer.unbindAll();
+    authContainer.load(AuthModule);
+  });
+
+  afterEach(() => {
+    authContainer.unbindAll();
+  });
+
+  it("resolves IUsersRepository to MockUsersRepository by default", () => {
+    const repo = authContainer.get<IUsersRepository>(
+      AUTH_SYMBOLS.IUsersRepository,
+    );
+    expect(repo).toBeInstanceOf(MockUsersRepository);
+  });
+
+  it("resolves IAuthenticationService to MockAuthenticationService by default", () => {
+    const service = authContainer.get<IAuthenticationService>(
+      AUTH_SYMBOLS.IAuthenticationService,
+    );
+    expect(service).toBeInstanceOf(MockAuthenticationService);
+  });
+
+  it("authentication service receives users repository via constructor injection", async () => {
+    const service = authContainer.get<IAuthenticationService>(
+      AUTH_SYMBOLS.IAuthenticationService,
+    );
+    // The service should be able to validate against the seeded users
+    const { session, cookie } = await service.createSession({
+      id: "1",
+      username: "alice",
+      passwordHash: "hashed_password_alice",
+    });
+    expect(session.userId).toBe("1");
+    expect(cookie.value).toBe(session.id);
+
+    // After session creation, validateSession should resolve user via the repo
+    const validated = await service.validateSession(session.id);
+    expect(validated.user.username).toBe("alice");
+  });
+});
diff --git a/packages/auth/src/di/container.ts b/packages/auth/src/di/container.ts
new file mode 100644
index 0000000..209254b
--- /dev/null
+++ b/packages/auth/src/di/container.ts
@@ -0,0 +1,6 @@
+import "reflect-metadata";
+import { Container } from "inversify";
+import { AuthModule } from "./module";
+
+export const authContainer = new Container({ defaultScope: "Singleton" });
+authContainer.load(AuthModule);
diff --git a/packages/auth/src/di/module.ts b/packages/auth/src/di/module.ts
new file mode 100644
index 0000000..a6cbd2c
--- /dev/null
+++ b/packages/auth/src/di/module.ts
@@ -0,0 +1,14 @@
+import { ContainerModule, type interfaces } from "inversify";
+
+import type { IUsersRepository } from "../application/repositories/users-repository.interface";
+import type { IAuthenticationService } from "../application/services/authentication-service.interface";
+import { MockUsersRepository } from "../infrastructure/repositories/mock-users.repository";
+import { MockAuthenticationService } from "../infrastructure/services/mock-authentication.service";
+import { AUTH_SYMBOLS } from "./symbols";
+
+export const AuthModule = new ContainerModule((bind: interfaces.Bind) => {
+  bind<IUsersRepository>(AUTH_SYMBOLS.IUsersRepository).to(MockUsersRepository);
+  bind<IAuthenticationService>(AUTH_SYMBOLS.IAuthenticationService).to(
+    MockAuthenticationService,
+  );
+});
diff --git a/packages/auth/src/di/symbols.ts b/packages/auth/src/di/symbols.ts
new file mode 100644
index 0000000..759f31d
--- /dev/null
+++ b/packages/auth/src/di/symbols.ts
@@ -0,0 +1,4 @@
+export const AUTH_SYMBOLS = {
+  IUsersRepository: Symbol.for("auth:IUsersRepository"),
+  IAuthenticationService: Symbol.for("auth:IAuthenticationService"),
+} as const;