diff --git a/ApiCore-Backend/src/app.module.ts b/ApiCore-Backend/src/app.module.ts
index b12efd2..0fa342b 100644
--- a/ApiCore-Backend/src/app.module.ts
+++ b/ApiCore-Backend/src/app.module.ts
@@ -25,6 +25,7 @@ import { QrModule } from './qr/qr.module';
 import { ProductsModule } from './products/products.module';
 import { BottlingModule } from './bottling/bottling.module';
 import { EquipmentModule } from './equipment/equipment.module';
+import { CalendarModule } from './calendar/calendar.module';
 import { JwtAuthGuard } from './auth/guards/jwt-auth.guard';
 import { RolesGuard } from './auth/guards/roles.guard';
 
@@ -55,6 +56,7 @@ import { RolesGuard } from './auth/guards/roles.guard';
     ProductsModule,
     BottlingModule,
     EquipmentModule,
+    CalendarModule,
   ],
   controllers: [],
   providers: [
diff --git a/ApiCore-Backend/src/calendar/calendar.controller.ts b/ApiCore-Backend/src/calendar/calendar.controller.ts
new file mode 100644
index 0000000..1cfbc27
--- /dev/null
+++ b/ApiCore-Backend/src/calendar/calendar.controller.ts
@@ -0,0 +1,28 @@
+import { BadRequestException, Controller, Get, Query } from '@nestjs/common';
+import { ApiBearerAuth, ApiTags } from '@nestjs/swagger';
+import { CalendarService } from './calendar.service';
+
+@ApiTags('calendar')
+@ApiBearerAuth()
+@Controller('calendar')
+export class CalendarController {
+  constructor(private readonly calendarService: CalendarService) {}
+
+  @Get()
+  getEvents(
+    @Query('from') from: string,
+    @Query('to') to: string,
+    @Query('apiaryId') apiaryId?: string,
+  ) {
+    if (!from || !to) {
+      throw new BadRequestException(
+        'Query parameters from and to are required',
+      );
+    }
+    return this.calendarService.getEvents({
+      from: new Date(from),
+      to: new Date(to),
+      apiaryId,
+    });
+  }
+}
diff --git a/ApiCore-Backend/src/calendar/calendar.module.ts b/ApiCore-Backend/src/calendar/calendar.module.ts
new file mode 100644
index 0000000..674b0b8
--- /dev/null
+++ b/ApiCore-Backend/src/calendar/calendar.module.ts
@@ -0,0 +1,9 @@
+import { Module } from '@nestjs/common';
+import { CalendarController } from './calendar.controller';
+import { CalendarService } from './calendar.service';
+
+@Module({
+  controllers: [CalendarController],
+  providers: [CalendarService],
+})
+export class CalendarModule {}
diff --git a/ApiCore-Backend/src/calendar/calendar.service.spec.ts b/ApiCore-Backend/src/calendar/calendar.service.spec.ts
new file mode 100644
index 0000000..8b507bf
--- /dev/null
+++ b/ApiCore-Backend/src/calendar/calendar.service.spec.ts
@@ -0,0 +1,85 @@
+import { CalendarService } from './calendar.service';
+import { PrismaService } from '../prisma/prisma.service';
+
+describe('CalendarService', () => {
+  let service: CalendarService;
+  let prisma: {
+    task: { findMany: jest.Mock };
+    inspection: { findMany: jest.Mock };
+    treatment: { findMany: jest.Mock };
+    feeding: { findMany: jest.Mock };
+    harvest: { findMany: jest.Mock };
+    queenColonyHistory: { findMany: jest.Mock };
+  };
+
+  beforeEach(() => {
+    prisma = {
+      task: { findMany: jest.fn().mockResolvedValue([]) },
+      inspection: { findMany: jest.fn().mockResolvedValue([]) },
+      treatment: { findMany: jest.fn().mockResolvedValue([]) },
+      feeding: { findMany: jest.fn().mockResolvedValue([]) },
+      harvest: { findMany: jest.fn().mockResolvedValue([]) },
+      queenColonyHistory: { findMany: jest.fn().mockResolvedValue([]) },
+    };
+    service = new CalendarService(prisma as unknown as PrismaService);
+  });
+
+  it('merges tasks, inspections, and harvests into one sorted event list', async () => {
+    prisma.task.findMany.mockResolvedValueOnce([
+      { id: 't1', title: 'Kontrolle', dueDate: new Date('2026-06-05') },
+    ]);
+    prisma.inspection.findMany.mockResolvedValueOnce([
+      {
+        id: 'i1',
+        date: new Date('2026-06-01'),
+        colonyId: 'c1',
+        colony: { code: 'V-001' },
+      },
+    ]);
+    prisma.harvest.findMany.mockResolvedValueOnce([
+      { id: 'h1', date: new Date('2026-06-10'), apiaryId: 'a1' },
+    ]);
+
+    const events = await service.getEvents({
+      from: new Date('2026-06-01'),
+      to: new Date('2026-06-30'),
+    });
+
+    expect(events.map((event) => event.type)).toEqual([
+      'INSPECTION',
+      'TASK',
+      'HARVEST',
+    ]);
+  });
+
+  it('filters colony-linked events by apiary when apiaryId is given', async () => {
+    await service.getEvents({
+      from: new Date('2026-06-01'),
+      to: new Date('2026-06-30'),
+      apiaryId: 'a1',
+    });
+
+    const [[inspectionArg]] = prisma.inspection.findMany.mock.calls as [
+      [{ where: { colony?: { apiaryId?: string } } }],
+    ];
+    expect(inspectionArg.where.colony).toEqual({ apiaryId: 'a1' });
+
+    const [[harvestArg]] = prisma.harvest.findMany.mock.calls as [
+      [{ where: { apiaryId?: string } }],
+    ];
+    expect(harvestArg.where.apiaryId).toBe('a1');
+  });
+
+  it('excludes tasks without a due date', async () => {
+    prisma.task.findMany.mockResolvedValueOnce([
+      { id: 't1', title: 'Ohne Datum', dueDate: null },
+    ]);
+
+    const events = await service.getEvents({
+      from: new Date('2026-06-01'),
+      to: new Date('2026-06-30'),
+    });
+
+    expect(events).toHaveLength(0);
+  });
+});
diff --git a/ApiCore-Backend/src/calendar/calendar.service.ts b/ApiCore-Backend/src/calendar/calendar.service.ts
new file mode 100644
index 0000000..3aa5ec4
--- /dev/null
+++ b/ApiCore-Backend/src/calendar/calendar.service.ts
@@ -0,0 +1,125 @@
+import { Injectable } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+
+export type CalendarEventType =
+  | 'TASK'
+  | 'INSPECTION'
+  | 'TREATMENT'
+  | 'FEEDING'
+  | 'HARVEST'
+  | 'QUEEN_ASSIGNMENT';
+
+export interface CalendarEvent {
+  id: string;
+  type: CalendarEventType;
+  date: Date;
+  title: string;
+  relatedType: string;
+  relatedId: string;
+}
+
+export interface CalendarQuery {
+  from: Date;
+  to: Date;
+  apiaryId?: string;
+}
+
+@Injectable()
+export class CalendarService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async getEvents(query: CalendarQuery): Promise<CalendarEvent[]> {
+    const { from, to, apiaryId } = query;
+    const colonyFilter = apiaryId ? { colony: { apiaryId } } : {};
+
+    const [
+      tasks,
+      inspections,
+      treatments,
+      feedings,
+      harvests,
+      queenAssignments,
+    ] = await Promise.all([
+      this.prisma.task.findMany({
+        where: { dueDate: { gte: from, lte: to } },
+      }),
+      this.prisma.inspection.findMany({
+        where: { date: { gte: from, lte: to }, ...colonyFilter },
+        include: { colony: true },
+      }),
+      this.prisma.treatment.findMany({
+        where: { date: { gte: from, lte: to }, ...colonyFilter },
+        include: { colony: true },
+      }),
+      this.prisma.feeding.findMany({
+        where: { date: { gte: from, lte: to }, ...colonyFilter },
+        include: { colony: true },
+      }),
+      this.prisma.harvest.findMany({
+        where: {
+          date: { gte: from, lte: to },
+          ...(apiaryId ? { apiaryId } : {}),
+        },
+      }),
+      this.prisma.queenColonyHistory.findMany({
+        where: { startDate: { gte: from, lte: to }, ...colonyFilter },
+        include: { colony: true, queen: true },
+      }),
+    ]);
+
+    const events: CalendarEvent[] = [
+      ...tasks
+        .filter((task) => task.dueDate !== null)
+        .map((task) => ({
+          id: task.id,
+          type: 'TASK' as const,
+          date: task.dueDate!,
+          title: task.title,
+          relatedType: 'Task',
+          relatedId: task.id,
+        })),
+      ...inspections.map((inspection) => ({
+        id: inspection.id,
+        type: 'INSPECTION' as const,
+        date: inspection.date,
+        title: `Durchsicht ${inspection.colony.code}`,
+        relatedType: 'Colony',
+        relatedId: inspection.colonyId,
+      })),
+      ...treatments.map((treatment) => ({
+        id: treatment.id,
+        type: 'TREATMENT' as const,
+        date: treatment.date,
+        title: `Behandlung ${treatment.colony.code} · ${treatment.product}`,
+        relatedType: 'Colony',
+        relatedId: treatment.colonyId,
+      })),
+      ...feedings.map((feeding) => ({
+        id: feeding.id,
+        type: 'FEEDING' as const,
+        date: feeding.date,
+        title: `Fütterung ${feeding.colony.code}`,
+        relatedType: 'Colony',
+        relatedId: feeding.colonyId,
+      })),
+      ...harvests.map((harvest) => ({
+        id: harvest.id,
+        type: 'HARVEST' as const,
+        date: harvest.date,
+        title: 'Ernte',
+        relatedType: 'Apiary',
+        relatedId: harvest.apiaryId,
+      })),
+      ...queenAssignments.map((assignment) => ({
+        id: assignment.id,
+        type: 'QUEEN_ASSIGNMENT' as const,
+        date: assignment.startDate,
+        title: `Königin ${assignment.queen.code} → ${assignment.colony.code}`,
+        relatedType: 'Queen',
+        relatedId: assignment.queenId,
+      })),
+    ];
+
+    return events.sort((a, b) => a.date.getTime() - b.date.getTime());
+  }
+}
diff --git a/ApiCore-Backend/test/calendar.e2e-spec.ts b/ApiCore-Backend/test/calendar.e2e-spec.ts
new file mode 100644
index 0000000..6390bd1
--- /dev/null
+++ b/ApiCore-Backend/test/calendar.e2e-spec.ts
@@ -0,0 +1,93 @@
+import { INestApplication } from '@nestjs/common';
+import * as bcrypt from 'bcryptjs';
+import request from 'supertest';
+import { App } from 'supertest/types';
+import { PrismaService } from '../src/prisma/prisma.service';
+import { createTestApp } from './utils/create-test-app';
+import { login } from './utils/api';
+
+interface CalendarEventBody {
+  type: string;
+  title: string;
+}
+
+describe('Calendar (e2e)', () => {
+  let app: INestApplication<App>;
+  let prisma: PrismaService;
+  const beekeeperEmail = `calendar-e2e-beekeeper-${Date.now()}@example.com`;
+  const password = 'SuperSecret123!';
+  let beekeeperId: string;
+  let beekeeperToken: string;
+  let apiaryId: string;
+  let colonyId: string;
+  let taskId: string;
+
+  beforeAll(async () => {
+    app = await createTestApp();
+    prisma = app.get(PrismaService);
+
+    const passwordHash = await bcrypt.hash(password, 12);
+    const beekeeper = await prisma.user.create({
+      data: {
+        email: beekeeperEmail,
+        passwordHash,
+        name: 'Beekeeper',
+        role: 'BEEKEEPER',
+      },
+    });
+    beekeeperId = beekeeper.id;
+    beekeeperToken = (await login(app, beekeeperEmail, password)).accessToken;
+
+    const apiary = await prisma.apiary.create({
+      data: { name: `Stand ${Date.now()}` },
+    });
+    apiaryId = apiary.id;
+    const colony = await prisma.colony.create({
+      data: {
+        code: `V-${Date.now()}`,
+        apiaryId,
+        colonyType: 'PRODUCTION_COLONY',
+      },
+    });
+    colonyId = colony.id;
+    const task = await prisma.task.create({
+      data: {
+        title: `Kalendertest ${Date.now()}`,
+        dueDate: new Date('2027-06-15'),
+        createdByUserId: beekeeperId,
+      },
+    });
+    taskId = task.id;
+  });
+
+  afterAll(async () => {
+    await prisma.task.deleteMany({ where: { id: taskId } });
+    await prisma.colony.deleteMany({ where: { id: colonyId } });
+    await prisma.apiary.deleteMany({ where: { id: apiaryId } });
+    await prisma.refreshToken.deleteMany({ where: { userId: beekeeperId } });
+    await prisma.auditLog.deleteMany({ where: { userId: beekeeperId } });
+    await prisma.user.deleteMany({ where: { id: beekeeperId } });
+    await app.close();
+  });
+
+  it('rejects the request when from/to are missing', () => {
+    return request(app.getHttpServer())
+      .get('/api/v1/calendar')
+      .set('Authorization', `Bearer ${beekeeperToken}`)
+      .expect(400);
+  });
+
+  it('returns events for a task due within the queried range', async () => {
+    const response = await request(app.getHttpServer())
+      .get('/api/v1/calendar?from=2027-06-01&to=2027-06-30')
+      .set('Authorization', `Bearer ${beekeeperToken}`)
+      .expect(200);
+    const events = response.body as CalendarEventBody[];
+    expect(
+      events.some(
+        (event) =>
+          event.type === 'TASK' && event.title.includes('Kalendertest'),
+      ),
+    ).toBe(true);
+  });
+});
diff --git a/TASKS.md b/TASKS.md
index 9723d8b..90e62f8 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -203,7 +203,7 @@ Reihenfolge = Bau-Reihenfolge. Gleiche Haken-Regel wie MVP: erst setzen, wenn Li
 - Backend: `CalendarModule` – aggregiert Durchsichten, Aufgaben, Behandlungen, Fütterungen, Ernten, Königinnenarbeiten in einem Zeitfenster
 - Endpunkte: `GET /api/v1/calendar?from=&to=&apiaryId=`
 - Frontend: `/calendar` (Monats-/Wochenansicht)
-- [ ] Backend-Modul fertig, getestet, grün, committet
+- [x] Backend-Modul fertig, getestet, grün, committet
 - [ ] Frontend-Views fertig, getestet, grün, committet
 
 ### 26. Benachrichtigungssystem