diff --git a/backend/src/ Message/ Message-thread.entity.ts b/backend/src/ Message/ Message-thread.entity.ts
new file mode 100644
index 0000000..1827596
--- /dev/null
+++ b/backend/src/ Message/ Message-thread.entity.ts	
@@ -0,0 +1,32 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  OneToMany,
+  CreateDateColumn,
+  Index,
+} from 'typeorm';
+import { Message } from './message.entity';
+
+@Entity('message_threads')
+@Index(['lastMessageAt'])
+export class MessageThread {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  /**
+   * JSON array of User UUIDs who are participants in this thread.
+   * Stored as JSONB for flexible multi-participant support.
+   */
+  @Column({ type: 'jsonb' })
+  participantIds: string[];
+
+  @Column({ type: 'timestamptz', nullable: true })
+  lastMessageAt: Date | null;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  createdAt: Date;
+
+  @OneToMany(() => Message, (msg) => msg.thread)
+  messages: Message[];
+}
\ No newline at end of file
diff --git a/backend/src/ Message/Message.entity.ts b/backend/src/ Message/Message.entity.ts
new file mode 100644
index 0000000..0f468d6
--- /dev/null
+++ b/backend/src/ Message/Message.entity.ts	
@@ -0,0 +1,48 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  ManyToOne,
+  JoinColumn,
+  CreateDateColumn,
+  Index,
+} from 'typeorm';
+import { MessageThread } from './message-thread.entity';
+import { User } from '../../../users/entities/user.entity';
+
+@Entity('messages')
+@Index(['threadId'])
+@Index(['senderUserId'])
+@Index(['isRead'])
+export class Message {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @Column({ type: 'uuid' })
+  threadId: string;
+
+  @ManyToOne(() => MessageThread, (thread) => thread.messages, { onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'threadId' })
+  thread: MessageThread;
+
+  @Column({ type: 'uuid' })
+  senderUserId: string;
+
+  @ManyToOne(() => User, { onDelete: 'RESTRICT' })
+  @JoinColumn({ name: 'senderUserId' })
+  sender: User;
+
+  @Column({ type: 'text' })
+  body: string;
+
+  /**
+   * Tracks whether the message has been read.
+   * Note: in a multi-participant thread, this is a per-message global flag.
+   * For per-user read receipts, extend to a separate read_receipts table.
+   */
+  @Column({ type: 'boolean', default: false })
+  isRead: boolean;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  sentAt: Date;
+}
\ No newline at end of file
diff --git a/backend/src/ Message/Messaging.controller.ts b/backend/src/ Message/Messaging.controller.ts
new file mode 100644
index 0000000..3befe4d
--- /dev/null
+++ b/backend/src/ Message/Messaging.controller.ts	
@@ -0,0 +1,84 @@
+import {
+  Body,
+  Controller,
+  Get,
+  Param,
+  ParseUUIDPipe,
+  Patch,
+  Post,
+  Query,
+} from '@nestjs/common';
+import { MessagingService } from './messaging.service';
+import { CurrentUser } from '../auth/decorators/current.user.decorators';
+import { User } from '../users/entities/user.entity';
+import { CreateThreadDto, MessagePaginationDto, SendMessageDto } from './dto/messaging.dto';
+
+@Controller('messages')
+export class MessagingController {
+  constructor(private readonly messagingService: MessagingService) {}
+
+  /**
+   * POST /messages/threads
+   * Start a new thread with one or more participants.
+   */
+  @Post('threads')
+  createThread(@Body() dto: CreateThreadDto, @CurrentUser() user: User) {
+    return this.messagingService.createThread(dto, user.id);
+  }
+
+  /**
+   * GET /messages/threads
+   * List all threads for the current user, sorted by lastMessageAt desc.
+   */
+  @Get('threads')
+  listThreads(@CurrentUser() user: User) {
+    return this.messagingService.listThreads(user.id);
+  }
+
+  /**
+   * GET /messages/threads/:id/messages
+   * Paginated message history for a thread (participants only).
+   */
+  @Get('threads/:id/messages')
+  getMessages(
+    @Param('id', ParseUUIDPipe) threadId: string,
+    @CurrentUser() user: User,
+    @Query() pagination: MessagePaginationDto,
+  ) {
+    return this.messagingService.getThreadMessages(threadId, user.id, pagination);
+  }
+
+  /**
+   * POST /messages/threads/:id/messages
+   * Send a message to a thread; emits new-message WS event.
+   */
+  @Post('threads/:id/messages')
+  sendMessage(
+    @Param('id', ParseUUIDPipe) threadId: string,
+    @Body() dto: SendMessageDto,
+    @CurrentUser() user: User,
+  ) {
+    return this.messagingService.sendMessage(threadId, dto, user.id);
+  }
+
+  /**
+   * PATCH /messages/threads/:id/read
+   * Mark all unread messages in the thread as read.
+   */
+  @Patch('threads/:id/read')
+  markRead(
+    @Param('id', ParseUUIDPipe) threadId: string,
+    @CurrentUser() user: User,
+  ) {
+    return this.messagingService.markAsRead(threadId, user.id);
+  }
+
+  /**
+   * GET /messages/unread-count
+   * Returns the total unread message count for badge display.
+   */
+  @Get('unread-count')
+  unreadCount(@CurrentUser() user: User) {
+    return this.messagingService.getUnreadCount(user.id);
+  }
+}
\ No newline at end of file
diff --git a/backend/src/ Message/Messaging.dto.ts b/backend/src/ Message/Messaging.dto.ts
new file mode 100644
index 0000000..35ef21b
--- /dev/null
+++ b/backend/src/ Message/Messaging.dto.ts	
@@ -0,0 +1,43 @@
+import {
+  IsArray,
+  IsNotEmpty,
+  IsString,
+  IsUUID,
+  ArrayMinSize,
+} from 'class-validator';
+import { Type } from 'class-transformer';
+import { IsOptional, IsInt, Min, Max } from 'class-validator';
+
+// ── Create Thread ─────────────────────────────────────────────────────────
+
+export class CreateThreadDto {
+  @IsArray()
+  @ArrayMinSize(1, { message: 'At least one participant is required' })
+  @IsUUID('4', { each: true })
+  participantIds: string[];
+}
+
+// ── Send Message ──────────────────────────────────────────────────────────
+
+export class SendMessageDto {
+  @IsString()
+  @IsNotEmpty({ message: 'Message body cannot be empty' })
+  body: string;
+}
+
+// ── Paginate Messages ─────────────────────────────────────────────────────
+
+export class MessagePaginationDto {
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  page?: number = 1;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  @Max(100)
+  limit?: number = 20;
+}
\ No newline at end of file
diff --git a/backend/src/ Message/Messaging.module.ts b/backend/src/ Message/Messaging.module.ts
new file mode 100644
index 0000000..e26d8fa
--- /dev/null
+++ b/backend/src/ Message/Messaging.module.ts	
@@ -0,0 +1,18 @@
+import { Module } from '@nestjs/common';
+import { TypeOrmModule } from '@nestjs/typeorm';
+import { MessageThread } from './entities/message-thread.entity';
+import { Message } from './entities/message.entity';
+import { MessagingService } from './messaging.service';
+import { MessagingController } from './messaging.controller';
+import { NotificationsModule } from '../notifications/notifications.module';
+
+@Module({
+  imports: [
+    TypeOrmModule.forFeature([MessageThread, Message]),
+    NotificationsModule,   // provides NotificationsGateway for WS emit
+  ],
+  controllers: [MessagingController],
+  providers: [MessagingService],
+  exports: [MessagingService],
+})
+export class MessagingModule {}
diff --git a/backend/src/ Message/Messaging.service.ts b/backend/src/ Message/Messaging.service.ts
new file mode 100644
index 0000000..70640ba
--- /dev/null
+++ b/backend/src/ Message/Messaging.service.ts	
@@ -0,0 +1,170 @@
+import {
+  ForbiddenException,
+  Injectable,
+  NotFoundException,
+} from '@nestjs/common';
+import { InjectRepository } from '@nestjs/typeorm';
+import { Repository } from 'typeorm';
+import { MessageThread } from './entities/message-thread.entity';
+import { Message } from './entities/message.entity';
+import { CreateThreadDto, SendMessageDto, MessagePaginationDto } from './dto/messaging.dto';
+import { NotificationsGateway } from '../notifications/gateway/notifications.gateway';
+
+@Injectable()
+export class MessagingService {
+  constructor(
+    @InjectRepository(MessageThread)
+    private readonly threadRepo: Repository<MessageThread>,
+    @InjectRepository(Message)
+    private readonly messageRepo: Repository<Message>,
+    private readonly notificationsGateway: NotificationsGateway,
+  ) {}
+
+  // ── POST /messages/threads ─────────────────────────────────────────────
+
+  async createThread(dto: CreateThreadDto, currentUserId: string): Promise<MessageThread> {
+    // Always include the creator in the participant list
+    const participantSet = new Set([currentUserId, ...dto.participantIds]);
+    const participantIds = Array.from(participantSet);
+
+    const thread = this.threadRepo.create({ participantIds, lastMessageAt: null });
+    return this.threadRepo.save(thread);
+  }
+
+  // ── GET /messages/threads ──────────────────────────────────────────────
+
+  async listThreads(userId: string): Promise<object[]> {
+    // Load threads the user participates in, with the latest message preview
+    const threads = await this.threadRepo
+      .createQueryBuilder('thread')
+      .where(':userId = ANY(thread.participantIds)', { userId })
+      .orderBy('thread.lastMessageAt', 'DESC', 'NULLS LAST')
+      .getMany();
+
+    // Fetch the last message for each thread
+    const results = await Promise.all(
+      threads.map(async (thread) => {
+        const lastMessage = await this.messageRepo.findOne({
+          where: { threadId: thread.id },
+          order: { sentAt: 'DESC' },
+          select: ['id', 'body', 'senderUserId', 'sentAt', 'isRead'],
+        });
+        return { ...thread, lastMessage: lastMessage ?? null };
+      }),
+    );
+
+    return results;
+  }
+
+  // ── GET /messages/threads/:id/messages ─────────────────────────────────
+
+  async getThreadMessages(
+    threadId: string,
+    userId: string,
+    pagination: MessagePaginationDto,
+  ): Promise<{ data: Message[]; total: number; page: number; limit: number }> {
+    const thread = await this.findThreadOrThrow(threadId);
+    this.assertParticipant(thread, userId);
+
+    const page  = pagination.page  ?? 1;
+    const limit = pagination.limit ?? 20;
+    const skip  = (page - 1) * limit;
+
+    const [data, total] = await this.messageRepo.findAndCount({
+      where: { threadId },
+      order: { sentAt: 'ASC' },
+      skip,
+      take: limit,
+    });
+
+    return { data, total, page, limit };
+  }
+
+  // ── POST /messages/threads/:id/messages ────────────────────────────────
+
+  async sendMessage(
+    threadId: string,
+    dto: SendMessageDto,
+    senderUserId: string,
+  ): Promise<Message> {
+    const thread = await this.findThreadOrThrow(threadId);
+    this.assertParticipant(thread, senderUserId);
+
+    const message = this.messageRepo.create({
+      threadId,
+      senderUserId,
+      body: dto.body,
+    });
+    const saved = await this.messageRepo.save(message);
+
+    // Update thread.lastMessageAt
+    await this.threadRepo.update(threadId, { lastMessageAt: saved.sentAt });
+
+    // Emit new-message WebSocket event to all participants
+    const payload = {
+      event:    'new-message',
+      threadId,
+      message:  { id: saved.id, body: saved.body, senderUserId, sentAt: saved.sentAt },
+    };
+
+    for (const participantId of thread.participantIds) {
+      this.notificationsGateway.server
+        ?.to(`user:${participantId}`)
+        .emit('new-message', payload);
+    }
+
+    return saved;
+  }
+
+  // ── PATCH /messages/threads/:id/read ──────────────────────────────────
+
+  async markAsRead(threadId: string, userId: string): Promise<{ updated: number }> {
+    const thread = await this.findThreadOrThrow(threadId);
+    this.assertParticipant(thread, userId);
+
+    const result = await this.messageRepo.update(
+      { threadId, isRead: false },
+      { isRead: true },
+    );
+
+    return { updated: result.affected ?? 0 };
+  }
+
+  // ── GET /messages/unread-count ─────────────────────────────────────────
+
+  async getUnreadCount(userId: string): Promise<{ unreadCount: number }> {
+    // Find all threads the user participates in
+    const threads = await this.threadRepo
+      .createQueryBuilder('thread')
+      .select('thread.id')
+      .where(':userId = ANY(thread.participantIds)', { userId })
+      .getMany();
+
+    if (threads.length === 0) return { unreadCount: 0 };
+
+    const threadIds = threads.map((t) => t.id);
+
+    const unreadCount = await this.messageRepo
+      .createQueryBuilder('msg')
+      .where('msg.threadId IN (:...threadIds)', { threadIds })
+      .andWhere('msg.isRead = false')
+      .andWhere('msg.senderUserId != :userId', { userId })   // don't count own messages
+      .getCount();
+
+    return { unreadCount };
+  }
+
+  // ── Helpers ────────────────────────────────────────────────────────────
+
+  private async findThreadOrThrow(threadId: string): Promise<MessageThread> {
+    const thread = await this.threadRepo.findOne({ where: { id: threadId } });
+    if (!thread) throw new NotFoundException(`Thread ${threadId} not found`);
+    return thread;
+  }
+
+  private assertParticipant(thread: MessageThread, userId: string): void {
+    if (!thread.participantIds.includes(userId)) {
+      throw new ForbiddenException('You are not a participant in this thread');
+    }
+  }
+}
\ No newline at end of file