diff --git a/apps/server/src/app.module.ts b/apps/server/src/app.module.ts
index 0a3d121..a2aa7b7 100644
--- a/apps/server/src/app.module.ts
+++ b/apps/server/src/app.module.ts
@@ -1,4 +1,4 @@
-import { Module } from '@nestjs/common';
+import { Module, NestModule, MiddlewareConsumer } from '@nestjs/common';
 import { APP_GUARD } from '@nestjs/core';
 import { ConfigModule, ConfigService } from '@nestjs/config';
 import { EventEmitterModule } from '@nestjs/event-emitter';
@@ -54,6 +54,8 @@ import { ClassroomRentalsModule } from './classroom-rentals/classroom-rentals.mo
 import { SyncModule } from './sync/sync.module';
 import { NotificationsModule } from './notifications/notifications.module';
 import { DepartmentsModule } from './departments/departments.module';
+import { CampusScope } from './common/campus-scope';
+import { CampusScopeMiddleware } from './common/campus-scope.middleware';
 
 @Module({
   imports: [
@@ -139,9 +141,14 @@ import { DepartmentsModule } from './departments/departments.module';
     DepartmentsModule,
   ],
   providers: [
+    CampusScope,
     { provide: APP_GUARD, useClass: ThrottlerGuard },
     { provide: APP_GUARD, useClass: JwtAuthGuard },
     { provide: APP_GUARD, useClass: PermissionGuard },
   ],
 })
-export class AppModule {}
+export class AppModule implements NestModule {
+  configure(consumer: MiddlewareConsumer) {
+    consumer.apply(CampusScopeMiddleware).forRoutes('*');
+  }
+}
diff --git a/apps/server/src/common/campus-scope.middleware.ts b/apps/server/src/common/campus-scope.middleware.ts
new file mode 100644
index 0000000..f07f8cd
--- /dev/null
+++ b/apps/server/src/common/campus-scope.middleware.ts
@@ -0,0 +1,13 @@
+import { Injectable, NestMiddleware } from '@nestjs/common';
+import { Request, Response, NextFunction } from 'express';
+import { CampusScope, CampusRequest } from './campus-scope';
+
+@Injectable()
+export class CampusScopeMiddleware implements NestMiddleware {
+  constructor(private readonly scope: CampusScope) {}
+
+  use(req: Request, _res: Response, next: NextFunction): void {
+    (req as CampusRequest).campusScope = this.scope;
+    next();
+  }
+}
diff --git a/apps/server/src/common/campus-scope.ts b/apps/server/src/common/campus-scope.ts
new file mode 100644
index 0000000..fc3616e
--- /dev/null
+++ b/apps/server/src/common/campus-scope.ts
@@ -0,0 +1,67 @@
+import { Injectable, Scope, Inject } from '@nestjs/common';
+import { REQUEST } from '@nestjs/core';
+import { In } from 'typeorm';
+import { Request } from 'express';
+import { DepartmentsService } from '../departments/departments.service';
+
+export interface CampusRequest extends Request {
+  user?: {
+    id: number;
+    isSuperAdmin?: boolean;
+  };
+  campusScope?: CampusScope;
+}
+
+@Injectable({ scope: Scope.REQUEST })
+export class CampusScope {
+  constructor(
+    @Inject(REQUEST) private req: CampusRequest,
+    private departmentsService: DepartmentsService,
+  ) {}
+
+  get userId(): number | undefined {
+    return this.req.user?.id;
+  }
+
+  get isSuperAdmin(): boolean {
+    return this.req.user?.isSuperAdmin ?? false;
+  }
+
+  get currentDepartmentId(): number | null {
+    const raw = this.req.headers?.['x-campus-id'];
+    if (raw === undefined) return null;
+    const str = Array.isArray(raw) ? raw[0] : raw;
+    if (!str) return null;
+    const id = parseInt(str, 10);
+    return Number.isNaN(id) ? null : id;
+  }
+
+  /** Appends departmentId filter to TypeORM find where conditions */
+  async filter<T extends Record<string, unknown>>(where: T): Promise<T> {
+    // Super admin with no campus selected → no filtering
+    if (this.isSuperAdmin && !this.currentDepartmentId) {
+      return where;
+    }
+
+    const ids = await this.getEffectiveScopeIds();
+    if (ids.length === 0) return where;
+
+    return { ...where, departmentId: In(ids) } as unknown as T;
+  }
+
+  private async getEffectiveScopeIds(): Promise<number[]> {
+    // Specific campus selected → campus + descendants
+    if (this.currentDepartmentId) {
+      return this.departmentsService.getDescendantIds(this.currentDepartmentId);
+    }
+
+    // No campus selected → all user departments + descendants
+    if (!this.userId) return [];
+
+    const userDeptIds = await this.departmentsService.getUserDepartments(this.userId);
+    const allIds = await Promise.all(
+      userDeptIds.map((id) => this.departmentsService.getDescendantIds(id)),
+    );
+    return [...new Set(allIds.flat())];
+  }
+}