diff --git a/models/__init__.py b/models/__init__.py
new file mode 100644
index 0000000..fa2b68a
--- /dev/null
+++ b/models/__init__.py
@@ -0,0 +1,5 @@
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    pass
diff --git a/models/category.py b/models/category.py
new file mode 100644
index 0000000..e811af2
--- /dev/null
+++ b/models/category.py
@@ -0,0 +1,24 @@
+from sqlalchemy import Column, ForeignKey, Integer, String, UniqueConstraint
+from sqlalchemy.orm import relationship
+
+from models import Base
+
+
+class Category(Base):
+    __tablename__ = "categories"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(String(50), unique=True, nullable=False)
+
+    words = relationship("CategoryWord", back_populates="category")
+
+
+class CategoryWord(Base):
+    __tablename__ = "category_words"
+    __table_args__ = (UniqueConstraint("category_id", "word"),)
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    category_id = Column(Integer, ForeignKey("categories.id"), nullable=False)
+    word = Column(String(20), nullable=False)
+
+    category = relationship("Category", back_populates="words")
diff --git a/models/game.py b/models/game.py
new file mode 100644
index 0000000..3262fe8
--- /dev/null
+++ b/models/game.py
@@ -0,0 +1,47 @@
+import uuid
+from datetime import datetime, timezone
+
+from sqlalchemy import (
+    Boolean,
+    Column,
+    DateTime,
+    ForeignKey,
+    Integer,
+    String,
+)
+from sqlalchemy.orm import relationship
+from sqlalchemy.types import JSON
+
+from models import Base
+
+
+class Game(Base):
+    __tablename__ = "games"
+
+    id = Column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    category_id = Column(Integer, ForeignKey("categories.id"), nullable=False)
+    board_size = Column(Integer, nullable=False, default=10)
+    grid = Column(JSON, nullable=False)
+    status = Column(String(20), nullable=False, default="in_progress")
+    started_at = Column(
+        DateTime, nullable=False, default=lambda: datetime.now(timezone.utc)
+    )
+    completed_at = Column(DateTime, nullable=True)
+
+    category = relationship("Category")
+    words = relationship("Word", back_populates="game")
+
+
+class Word(Base):
+    __tablename__ = "words"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    game_id = Column(String(36), ForeignKey("games.id"), nullable=False)
+    text = Column(String(20), nullable=False)
+    start_row = Column(Integer, nullable=False)
+    start_col = Column(Integer, nullable=False)
+    direction = Column(String(2), nullable=False)
+    found = Column(Boolean, nullable=False, default=False)
+    found_at = Column(DateTime, nullable=True)
+
+    game = relationship("Game", back_populates="words")
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..f6b8ae7
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,16 @@
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+from models import Base
+
+
+@pytest.fixture
+def db_session():
+    engine = create_engine("sqlite:///:memory:")
+    Base.metadata.create_all(engine)
+    Session = sessionmaker(bind=engine)
+    session = Session()
+    yield session
+    session.close()
+    engine.dispose()
diff --git a/tests/unit/test_models.py b/tests/unit/test_models.py
new file mode 100644
index 0000000..492938f
--- /dev/null
+++ b/tests/unit/test_models.py
@@ -0,0 +1,74 @@
+from models.category import Category, CategoryWord
+from models.game import Game, Word
+
+
+def test_create_category(db_session):
+    cat = Category(name="animals")
+    db_session.add(cat)
+    db_session.commit()
+    assert cat.id is not None
+    assert cat.name == "animals"
+
+
+def test_create_category_word(db_session):
+    cat = Category(name="animals")
+    db_session.add(cat)
+    db_session.flush()
+    word = CategoryWord(category_id=cat.id, word="TIGER")
+    db_session.add(word)
+    db_session.commit()
+    assert word.category_id == cat.id
+    assert word.word == "TIGER"
+
+
+def test_create_game(db_session):
+    cat = Category(name="animals")
+    db_session.add(cat)
+    db_session.flush()
+    game = Game(
+        category_id=cat.id,
+        board_size=10,
+        grid=[["A"] * 10 for _ in range(10)],
+    )
+    db_session.add(game)
+    db_session.commit()
+    assert game.id is not None
+    assert len(game.id) == 36  # UUID
+    assert game.status == "in_progress"
+    assert game.started_at is not None
+    assert game.completed_at is None
+
+
+def test_create_word(db_session):
+    cat = Category(name="animals")
+    db_session.add(cat)
+    db_session.flush()
+    game = Game(category_id=cat.id, board_size=10, grid=[])
+    db_session.add(game)
+    db_session.flush()
+    word = Word(
+        game_id=game.id,
+        text="TIGER",
+        start_row=0,
+        start_col=0,
+        direction="E",
+    )
+    db_session.add(word)
+    db_session.commit()
+    assert word.found is False
+    assert word.found_at is None
+
+
+def test_game_words_relationship(db_session):
+    cat = Category(name="animals")
+    db_session.add(cat)
+    db_session.flush()
+    game = Game(category_id=cat.id, board_size=10, grid=[])
+    db_session.add(game)
+    db_session.flush()
+    w1 = Word(game_id=game.id, text="TIGER", start_row=0, start_col=0, direction="E")
+    w2 = Word(game_id=game.id, text="LION", start_row=1, start_col=0, direction="S")
+    db_session.add_all([w1, w2])
+    db_session.commit()
+    db_session.refresh(game)
+    assert len(game.words) == 2