diff --git a/backend/src/domain/entities/__init__.py b/backend/src/domain/entities/__init__.py
new file mode 100644
index 0000000..c3a6d2e
--- /dev/null
+++ b/backend/src/domain/entities/__init__.py
@@ -0,0 +1,4 @@
+"""
+Domain entities
+"""
+
diff --git a/backend/src/domain/entities/collection.py b/backend/src/domain/entities/collection.py
new file mode 100644
index 0000000..abfc3a0
--- /dev/null
+++ b/backend/src/domain/entities/collection.py
@@ -0,0 +1,26 @@
+"""
+Доменная сущность Collection
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+
+
+class Collection:
+    """Каталог документов"""
+    
+    def __init__(
+        self,
+        name: str,
+        owner_id: UUID,
+        description: str = "",
+        is_public: bool = False,
+        collection_id: UUID | None = None,
+        created_at: datetime | None = None
+    ):
+        self.collection_id = collection_id or uuid4()
+        self.name = name
+        self.description = description
+        self.owner_id = owner_id
+        self.is_public = is_public
+        self.created_at = created_at or datetime.utcnow()
+
diff --git a/backend/src/domain/entities/collection_access.py b/backend/src/domain/entities/collection_access.py
new file mode 100644
index 0000000..df4cd0a
--- /dev/null
+++ b/backend/src/domain/entities/collection_access.py
@@ -0,0 +1,22 @@
+"""
+Доменная сущность CollectionAccess
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+
+
+class CollectionAccess:
+    """Доступ пользователя к коллекции"""
+    
+    def __init__(
+        self,
+        user_id: UUID,
+        collection_id: UUID,
+        access_id: UUID | None = None,
+        created_at: datetime | None = None
+    ):
+        self.access_id = access_id or uuid4()
+        self.user_id = user_id
+        self.collection_id = collection_id
+        self.created_at = created_at or datetime.utcnow()
+
diff --git a/backend/src/domain/entities/conversation.py b/backend/src/domain/entities/conversation.py
new file mode 100644
index 0000000..ffe42cc
--- /dev/null
+++ b/backend/src/domain/entities/conversation.py
@@ -0,0 +1,28 @@
+"""
+Доменная сущность Conversation
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+
+
+class Conversation:
+    """Беседа пользователя с ИИ"""
+    
+    def __init__(
+        self,
+        user_id: UUID,
+        collection_id: UUID,
+        conversation_id: UUID | None = None,
+        created_at: datetime | None = None,
+        updated_at: datetime | None = None
+    ):
+        self.conversation_id = conversation_id or uuid4()
+        self.user_id = user_id
+        self.collection_id = collection_id
+        self.created_at = created_at or datetime.utcnow()
+        self.updated_at = updated_at or datetime.utcnow()
+    
+    def update_timestamp(self):
+        """Обновить время последнего изменения"""
+        self.updated_at = datetime.utcnow()
+
diff --git a/backend/src/domain/entities/document.py b/backend/src/domain/entities/document.py
new file mode 100644
index 0000000..48bc95d
--- /dev/null
+++ b/backend/src/domain/entities/document.py
@@ -0,0 +1,27 @@
+"""
+Доменная сущность Document
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+from typing import Any
+
+
+class Document:
+    """Документ в коллекции"""
+    
+    def __init__(
+        self,
+        collection_id: UUID,
+        title: str,
+        content: str,
+        metadata: dict[str, Any] | None = None,
+        document_id: UUID | None = None,
+        created_at: datetime | None = None
+    ):
+        self.document_id = document_id or uuid4()
+        self.collection_id = collection_id
+        self.title = title
+        self.content = content
+        self.metadata = metadata or {}
+        self.created_at = created_at or datetime.utcnow()
+
diff --git a/backend/src/domain/entities/embedding.py b/backend/src/domain/entities/embedding.py
new file mode 100644
index 0000000..4da5977
--- /dev/null
+++ b/backend/src/domain/entities/embedding.py
@@ -0,0 +1,25 @@
+"""
+Доменная сущность Embedding
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+from typing import Any
+
+
+class Embedding:
+    """Эмбеддинг документа"""
+    
+    def __init__(
+        self,
+        document_id: UUID,
+        embedding: list[float] | None = None,
+        model_version: str = "",
+        embedding_id: UUID | None = None,
+        created_at: datetime | None = None
+    ):
+        self.embedding_id = embedding_id or uuid4()
+        self.document_id = document_id
+        self.embedding = embedding or []
+        self.model_version = model_version
+        self.created_at = created_at or datetime.utcnow()
+
diff --git a/backend/src/domain/entities/message.py b/backend/src/domain/entities/message.py
new file mode 100644
index 0000000..967f439
--- /dev/null
+++ b/backend/src/domain/entities/message.py
@@ -0,0 +1,35 @@
+"""
+Доменная сущность Message
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+from typing import Any
+from enum import Enum
+
+
+class MessageRole(str, Enum):
+    """Роли сообщений"""
+    USER = "user"
+    ASSISTANT = "assistant"
+    SYSTEM = "system"
+
+
+class Message:
+    """Сообщение в беседе"""
+    
+    def __init__(
+        self,
+        conversation_id: UUID,
+        content: str,
+        role: MessageRole,
+        sources: dict[str, Any] | None = None,
+        message_id: UUID | None = None,
+        created_at: datetime | None = None
+    ):
+        self.message_id = message_id or uuid4()
+        self.conversation_id = conversation_id
+        self.content = content
+        self.role = role
+        self.sources = sources or {}
+        self.created_at = created_at or datetime.utcnow()
+
diff --git a/backend/src/domain/entities/user.py b/backend/src/domain/entities/user.py
new file mode 100644
index 0000000..a9cc815
--- /dev/null
+++ b/backend/src/domain/entities/user.py
@@ -0,0 +1,33 @@
+"""
+Доменная сущность User
+"""
+from datetime import datetime
+from uuid import UUID, uuid4
+from enum import Enum
+
+
+class UserRole(str, Enum):
+    """Роли пользователей"""
+    USER = "user"
+    ADMIN = "admin"
+
+
+class User:
+    """Пользователь системы"""
+    
+    def __init__(
+        self,
+        telegram_id: str,
+        role: UserRole = UserRole.USER,
+        user_id: UUID | None = None,
+        created_at: datetime | None = None
+    ):
+        self.user_id = user_id or uuid4()
+        self.telegram_id = telegram_id
+        self.role = role
+        self.created_at = created_at or datetime.utcnow()
+    
+    def is_admin(self) -> bool:
+        """проверка, является ли пользователь администратором"""
+        return self.role == UserRole.ADMIN
+
diff --git a/backend/src/domain/repositories/__init__.py b/backend/src/domain/repositories/__init__.py
new file mode 100644
index 0000000..0647a45
--- /dev/null
+++ b/backend/src/domain/repositories/__init__.py
@@ -0,0 +1,4 @@
+"""
+Domain repositories interfaces
+"""
+
diff --git a/backend/src/domain/repositories/collection_access_repository.py b/backend/src/domain/repositories/collection_access_repository.py
new file mode 100644
index 0000000..765649e
--- /dev/null
+++ b/backend/src/domain/repositories/collection_access_repository.py
@@ -0,0 +1,47 @@
+"""
+Интерфейс репозитория для CollectionAccess
+"""
+from abc import ABC, abstractmethod
+from uuid import UUID
+from typing import Optional
+from src.domain.entities.collection_access import CollectionAccess
+
+
+class ICollectionAccessRepository(ABC):
+    """Интерфейс репозитория доступа к коллекциям"""
+    
+    @abstractmethod
+    async def create(self, access: CollectionAccess) -> CollectionAccess:
+        """Создать доступ"""
+        pass
+    
+    @abstractmethod
+    async def get_by_id(self, access_id: UUID) -> Optional[CollectionAccess]:
+        """Получить доступ по ID"""
+        pass
+    
+    @abstractmethod
+    async def delete(self, access_id: UUID) -> bool:
+        """Удалить доступ"""
+        pass
+    
+    @abstractmethod
+    async def delete_by_user_and_collection(self, user_id: UUID, collection_id: UUID) -> bool:
+        """Удалить доступ пользователя к коллекции"""
+        pass
+    
+    @abstractmethod
+    async def get_by_user_and_collection(self, user_id: UUID, collection_id: UUID) -> Optional[CollectionAccess]:
+        """Получить доступ пользователя к коллекции"""
+        pass
+    
+    @abstractmethod
+    async def list_by_user(self, user_id: UUID) -> list[CollectionAccess]:
+        """Получить доступы пользователя"""
+        pass
+    
+    @abstractmethod
+    async def list_by_collection(self, collection_id: UUID) -> list[CollectionAccess]:
+        """Получить доступы к коллекции"""
+        pass
+
diff --git a/backend/src/domain/repositories/collection_repository.py b/backend/src/domain/repositories/collection_repository.py
new file mode 100644
index 0000000..6e4e0a3
--- /dev/null
+++ b/backend/src/domain/repositories/collection_repository.py
@@ -0,0 +1,42 @@
+"""
+Интерфейс репозитория для Collection
+"""
+from abc import ABC, abstractmethod
+from uuid import UUID
+from typing import Optional
+from src.domain.entities.collection import Collection
+
+
+class ICollectionRepository(ABC):
+    """Интерфейс репозитория коллекций"""
+    
+    @abstractmethod
+    async def create(self, collection: Collection) -> Collection:
+        """Создать коллекцию"""
+        pass
+    
+    @abstractmethod
+    async def get_by_id(self, collection_id: UUID) -> Optional[Collection]:
+        """Получить коллекцию по ID"""
+        pass
+    
+    @abstractmethod
+    async def update(self, collection: Collection) -> Collection:
+        """Обновить коллекцию"""
+        pass
+    
+    @abstractmethod
+    async def delete(self, collection_id: UUID) -> bool:
+        """Удалить коллекцию"""
+        pass
+    
+    @abstractmethod
+    async def list_by_owner(self, owner_id: UUID, skip: int = 0, limit: int = 100) -> list[Collection]:
+        """Получить коллекции владельца"""
+        pass
+    
+    @abstractmethod
+    async def list_public(self, skip: int = 0, limit: int = 100) -> list[Collection]:
+        """Получить публичные коллекции"""
+        pass
+
diff --git a/backend/src/domain/repositories/conversation_repository.py b/backend/src/domain/repositories/conversation_repository.py
new file mode 100644
index 0000000..7eccd6a
--- /dev/null
+++ b/backend/src/domain/repositories/conversation_repository.py
@@ -0,0 +1,42 @@
+"""
+Интерфейс репозитория для Conversation
+"""
+from abc import ABC, abstractmethod
+from uuid import UUID
+from typing import Optional
+from src.domain.entities.conversation import Conversation
+
+
+class IConversationRepository(ABC):
+    """Интерфейс репозитория бесед"""
+    
+    @abstractmethod
+    async def create(self, conversation: Conversation) -> Conversation:
+        """Создать беседу"""
+        pass
+    
+    @abstractmethod
+    async def get_by_id(self, conversation_id: UUID) -> Optional[Conversation]:
+        """Получить беседу по ID"""
+        pass
+    
+    @abstractmethod
+    async def update(self, conversation: Conversation) -> Conversation:
+        """Обновить беседу"""
+        pass
+    
+    @abstractmethod
+    async def delete(self, conversation_id: UUID) -> bool:
+        """Удалить беседу"""
+        pass
+    
+    @abstractmethod
+    async def list_by_user(self, user_id: UUID, skip: int = 0, limit: int = 100) -> list[Conversation]:
+        """Получить беседы пользователя"""
+        pass
+    
+    @abstractmethod
+    async def list_by_collection(self, collection_id: UUID, skip: int = 0, limit: int = 100) -> list[Conversation]:
+        """Получить беседы по коллекции"""
+        pass
+
diff --git a/backend/src/domain/repositories/document_repository.py b/backend/src/domain/repositories/document_repository.py
new file mode 100644
index 0000000..68f4826
--- /dev/null
+++ b/backend/src/domain/repositories/document_repository.py
@@ -0,0 +1,37 @@
+"""
+Интерфейс репозитория для Document
+"""
+from abc import ABC, abstractmethod
+from uuid import UUID
+from typing import Optional
+from src.domain.entities.document import Document
+
+
+class IDocumentRepository(ABC):
+    """Интерфейс репозитория документов"""
+    
+    @abstractmethod
+    async def create(self, document: Document) -> Document:
+        """Создать документ"""
+        pass
+    
+    @abstractmethod
+    async def get_by_id(self, document_id: UUID) -> Optional[Document]:
+        """Получить документ по ID"""
+        pass
+    
+    @abstractmethod
+    async def update(self, document: Document) -> Document:
+        """Обновить документ"""
+        pass
+    
+    @abstractmethod
+    async def delete(self, document_id: UUID) -> bool:
+        """Удалить документ"""
+        pass
+    
+    @abstractmethod
+    async def list_by_collection(self, collection_id: UUID, skip: int = 0, limit: int = 100) -> list[Document]:
+        """Получить документы коллекции"""
+        pass
+
diff --git a/backend/src/domain/repositories/message_repository.py b/backend/src/domain/repositories/message_repository.py
new file mode 100644
index 0000000..d40d477
--- /dev/null
+++ b/backend/src/domain/repositories/message_repository.py
@@ -0,0 +1,37 @@
+"""
+Интерфейс репозитория для Message
+"""
+from abc import ABC, abstractmethod
+from uuid import UUID
+from typing import Optional
+from src.domain.entities.message import Message
+
+
+class IMessageRepository(ABC):
+    """Интерфейс репозитория сообщений"""
+    
+    @abstractmethod
+    async def create(self, message: Message) -> Message:
+        """Создать сообщение"""
+        pass
+    
+    @abstractmethod
+    async def get_by_id(self, message_id: UUID) -> Optional[Message]:
+        """Получить сообщение по ID"""
+        pass
+    
+    @abstractmethod
+    async def update(self, message: Message) -> Message:
+        """Обновить сообщение"""
+        pass
+    
+    @abstractmethod
+    async def delete(self, message_id: UUID) -> bool:
+        """Удалить сообщение"""
+        pass
+    
+    @abstractmethod
+    async def list_by_conversation(self, conversation_id: UUID, skip: int = 0, limit: int = 100) -> list[Message]:
+        """Получить сообщения беседы"""
+        pass
+
diff --git a/backend/src/domain/repositories/user_repository.py b/backend/src/domain/repositories/user_repository.py
new file mode 100644
index 0000000..a724816
--- /dev/null
+++ b/backend/src/domain/repositories/user_repository.py
@@ -0,0 +1,42 @@
+"""
+Интерфейс репозитория для User
+"""
+from abc import ABC, abstractmethod
+from uuid import UUID
+from typing import Optional
+from src.domain.entities.user import User
+
+
+class IUserRepository(ABC):
+    """Интерфейс репозитория пользователей"""
+    
+    @abstractmethod
+    async def create(self, user: User) -> User:
+        """Создать пользователя"""
+        pass
+    
+    @abstractmethod
+    async def get_by_id(self, user_id: UUID) -> Optional[User]:
+        """Получить пользователя по ID"""
+        pass
+    
+    @abstractmethod
+    async def get_by_telegram_id(self, telegram_id: str) -> Optional[User]:
+        """Получить пользователя по Telegram ID"""
+        pass
+    
+    @abstractmethod
+    async def update(self, user: User) -> User:
+        """Обновить пользователя"""
+        pass
+    
+    @abstractmethod
+    async def delete(self, user_id: UUID) -> bool:
+        """Удалить пользователя"""
+        pass
+    
+    @abstractmethod
+    async def list_all(self, skip: int = 0, limit: int = 100) -> list[User]:
+        """Получить список всех пользователей"""
+        pass
+
diff --git a/backend/src/infrastructure/database/__init__.py b/backend/src/infrastructure/database/__init__.py
new file mode 100644
index 0000000..0049886
--- /dev/null
+++ b/backend/src/infrastructure/database/__init__.py
@@ -0,0 +1,4 @@
+"""
+Database infrastructure
+"""
+
diff --git a/backend/src/infrastructure/database/base.py b/backend/src/infrastructure/database/base.py
new file mode 100644
index 0000000..8c19b37
--- /dev/null
+++ b/backend/src/infrastructure/database/base.py
@@ -0,0 +1,32 @@
+"""
+Базовые настройки базы данных
+"""
+from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
+from sqlalchemy.orm import declarative_base
+from src.shared.config import settings
+
+engine = create_async_engine(
+    settings.database_url.replace("postgresql://", "postgresql+asyncpg://"),
+    echo=settings.DEBUG,
+    future=True
+)
+
+AsyncSessionLocal = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+    autocommit=False,
+    autoflush=False
+)
+
+Base = declarative_base()
+
+
+async def get_db() -> AsyncSession:
+    """Dependency для получения сессии БД"""
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+        finally:
+            await session.close()
+
diff --git a/backend/src/infrastructure/database/models.py b/backend/src/infrastructure/database/models.py
new file mode 100644
index 0000000..b2312fe
--- /dev/null
+++ b/backend/src/infrastructure/database/models.py
@@ -0,0 +1,109 @@
+"""
+SQLAlchemy модели для базы данных
+"""
+from sqlalchemy import Column, String, Text, Boolean, DateTime, ForeignKey, JSON, Integer
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+from datetime import datetime
+import uuid
+from src.infrastructure.database.base import Base
+
+
+class UserModel(Base):
+    """Модель пользователя"""
+    __tablename__ = "users"
+    
+    user_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    telegram_id = Column(String, unique=True, nullable=False, index=True)
+    role = Column(String, nullable=False, default="user")
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    collections = relationship("CollectionModel", back_populates="owner", cascade="all, delete-orphan")
+    conversations = relationship("ConversationModel", back_populates="user", cascade="all, delete-orphan")
+    collection_accesses = relationship("CollectionAccessModel", back_populates="user", cascade="all, delete-orphan")
+
+
+class CollectionModel(Base):
+    """Модель коллекции"""
+    __tablename__ = "collections"
+    
+    collection_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    owner_id = Column(UUID(as_uuid=True), ForeignKey("users.user_id"), nullable=False)
+    is_public = Column(Boolean, nullable=False, default=False)
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    owner = relationship("UserModel", back_populates="collections")
+    documents = relationship("DocumentModel", back_populates="collection", cascade="all, delete-orphan")
+    conversations = relationship("ConversationModel", back_populates="collection", cascade="all, delete-orphan")
+    accesses = relationship("CollectionAccessModel", back_populates="collection", cascade="all, delete-orphan")
+
+
+class DocumentModel(Base):
+    """Модель документа"""
+    __tablename__ = "documents"
+    
+    document_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    collection_id = Column(UUID(as_uuid=True), ForeignKey("collections.collection_id"), nullable=False)
+    title = Column(String, nullable=False)
+    content = Column(Text, nullable=False)
+    document_metadata = Column("metadata", JSON, nullable=True, default={})
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    collection = relationship("CollectionModel", back_populates="documents")
+    embeddings = relationship("EmbeddingModel", back_populates="document", cascade="all, delete-orphan")
+
+
+class EmbeddingModel(Base):
+    """Модель эмбеддинга (заглушка)"""
+    __tablename__ = "embeddings"
+    
+    embedding_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    document_id = Column(UUID(as_uuid=True), ForeignKey("documents.document_id"), nullable=False)
+    embedding = Column(JSON, nullable=True)
+    model_version = Column(String, nullable=True)
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    document = relationship("DocumentModel", back_populates="embeddings")
+
+
+class ConversationModel(Base):
+    """Модель беседы"""
+    __tablename__ = "conversations"
+    
+    conversation_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.user_id"), nullable=False)
+    collection_id = Column(UUID(as_uuid=True), ForeignKey("collections.collection_id"), nullable=False)
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    updated_at = Column(DateTime, nullable=False, default=datetime.utcnow, onupdate=datetime.utcnow)
+
+    user = relationship("UserModel", back_populates="conversations")
+    collection = relationship("CollectionModel", back_populates="conversations")
+    messages = relationship("MessageModel", back_populates="conversation", cascade="all, delete-orphan")
+
+
+class MessageModel(Base):
+    """Модель сообщения"""
+    __tablename__ = "messages"
+    
+    message_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    conversation_id = Column(UUID(as_uuid=True), ForeignKey("conversations.conversation_id"), nullable=False)
+    content = Column(Text, nullable=False)
+    role = Column(String, nullable=False)
+    sources = Column(JSON, nullable=True, default={})
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    conversation = relationship("ConversationModel", back_populates="messages")
+
+
+class CollectionAccessModel(Base):
+    """Модель доступа к коллекции"""
+    __tablename__ = "collection_access"
+    
+    access_id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.user_id"), nullable=False)
+    collection_id = Column(UUID(as_uuid=True), ForeignKey("collections.collection_id"), nullable=False)
+    created_at = Column(DateTime, nullable=False, default=datetime.utcnow)
+    user = relationship("UserModel", back_populates="collection_accesses")
+    collection = relationship("CollectionModel", back_populates="accesses")
+    
+    __table_args__ = (
+        {"comment": "Уникальный доступ пользователя к коллекции"},
+    )
+