diff --git a/backend/app/main.py b/backend/app/main.py
index 92f75e8..073a173 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -43,6 +43,37 @@ app.add_middleware(
 )
 
 
+# Add security headers middleware
+@app.middleware("http")
+async def add_security_headers(request: Request, call_next):
+    """Add security headers to all responses"""
+    response = await call_next(request)
+
+    # Prevent clickjacking
+    response.headers["X-Frame-Options"] = "DENY"
+
+    # Prevent MIME type sniffing
+    response.headers["X-Content-Type-Options"] = "nosniff"
+
+    # Enable XSS protection
+    response.headers["X-XSS-Protection"] = "1; mode=block"
+
+    # Enforce HTTPS in production
+    if settings.ENVIRONMENT == "production":
+        response.headers["Strict-Transport-Security"] = "max-age=31536000; includeSubDomains"
+
+    # Content Security Policy
+    response.headers["Content-Security-Policy"] = "default-src 'self'; frame-ancestors 'none'"
+
+    # Permissions Policy (formerly Feature Policy)
+    response.headers["Permissions-Policy"] = "geolocation=(), microphone=(), camera=()"
+
+    # Referrer Policy
+    response.headers["Referrer-Policy"] = "strict-origin-when-cross-origin"
+
+    return response
+
+
 @app.get("/", response_class=HTMLResponse)
 async def root():
     return """
diff --git a/backend/app/models/user.py b/backend/app/models/user.py
index 783de85..a5aa604 100644
--- a/backend/app/models/user.py
+++ b/backend/app/models/user.py
@@ -1,4 +1,5 @@
-from sqlalchemy import Column, String, JSON, Boolean
+from sqlalchemy import Column, String, Boolean
+from sqlalchemy.dialects.postgresql import JSONB
 
 from .base import Base, TimestampMixin, UUIDMixin
 
@@ -6,14 +7,14 @@ from .base import Base, TimestampMixin, UUIDMixin
 class User(Base, UUIDMixin, TimestampMixin):
     __tablename__ = 'users'
 
-    email = Column(String, unique=True, nullable=False, index=True)
-    password_hash = Column(String, nullable=False)
-    first_name = Column(String, nullable=False, default="user")
-    last_name = Column(String, nullable=True)
-    phone_number = Column(String)
-    is_active = Column(Boolean, default=True, nullable=False)
-    is_superuser = Column(Boolean, default=False, nullable=False)
-    preferences = Column(JSON)
+    email = Column(String(255), unique=True, nullable=False, index=True)
+    password_hash = Column(String(255), nullable=False)
+    first_name = Column(String(100), nullable=False, default="user")
+    last_name = Column(String(100), nullable=True)
+    phone_number = Column(String(20))
+    is_active = Column(Boolean, default=True, nullable=False, index=True)
+    is_superuser = Column(Boolean, default=False, nullable=False, index=True)
+    preferences = Column(JSONB)
 
     def __repr__(self):
         return f"<User {self.email}>"
\ No newline at end of file
diff --git a/backend/tests/api/test_security_headers.py b/backend/tests/api/test_security_headers.py
new file mode 100644
index 0000000..51b295c
--- /dev/null
+++ b/backend/tests/api/test_security_headers.py
@@ -0,0 +1,94 @@
+# tests/api/test_security_headers.py
+import pytest
+from fastapi.testclient import TestClient
+from unittest.mock import patch
+
+from app.main import app
+
+
+@pytest.fixture
+def client():
+    """Create a FastAPI test client for the main app."""
+    # Mock get_db to avoid database connection issues
+    with patch("app.main.get_db") as mock_get_db:
+        def mock_session_generator():
+            from unittest.mock import MagicMock
+            mock_session = MagicMock()
+            mock_session.execute.return_value = None
+            mock_session.close.return_value = None
+            yield mock_session
+
+        mock_get_db.side_effect = lambda: mock_session_generator()
+        yield TestClient(app)
+
+
+class TestSecurityHeaders:
+    """Tests for security headers middleware"""
+
+    def test_x_frame_options_header(self, client):
+        """Test that X-Frame-Options header is set to DENY"""
+        response = client.get("/health")
+        assert "X-Frame-Options" in response.headers
+        assert response.headers["X-Frame-Options"] == "DENY"
+
+    def test_x_content_type_options_header(self, client):
+        """Test that X-Content-Type-Options header is set to nosniff"""
+        response = client.get("/health")
+        assert "X-Content-Type-Options" in response.headers
+        assert response.headers["X-Content-Type-Options"] == "nosniff"
+
+    def test_x_xss_protection_header(self, client):
+        """Test that X-XSS-Protection header is set"""
+        response = client.get("/health")
+        assert "X-XSS-Protection" in response.headers
+        assert response.headers["X-XSS-Protection"] == "1; mode=block"
+
+    def test_content_security_policy_header(self, client):
+        """Test that Content-Security-Policy header is set"""
+        response = client.get("/health")
+        assert "Content-Security-Policy" in response.headers
+        assert "default-src 'self'" in response.headers["Content-Security-Policy"]
+        assert "frame-ancestors 'none'" in response.headers["Content-Security-Policy"]
+
+    def test_permissions_policy_header(self, client):
+        """Test that Permissions-Policy header is set"""
+        response = client.get("/health")
+        assert "Permissions-Policy" in response.headers
+        assert "geolocation=()" in response.headers["Permissions-Policy"]
+        assert "microphone=()" in response.headers["Permissions-Policy"]
+        assert "camera=()" in response.headers["Permissions-Policy"]
+
+    def test_referrer_policy_header(self, client):
+        """Test that Referrer-Policy header is set"""
+        response = client.get("/health")
+        assert "Referrer-Policy" in response.headers
+        assert response.headers["Referrer-Policy"] == "strict-origin-when-cross-origin"
+
+    def test_strict_transport_security_not_in_development(self, client):
+        """Test that Strict-Transport-Security header is not set in development"""
+        from app.core.config import settings
+
+        # In development, HSTS should not be present
+        if settings.ENVIRONMENT == "development":
+            response = client.get("/health")
+            assert "Strict-Transport-Security" not in response.headers
+
+    def test_security_headers_on_all_endpoints(self, client):
+        """Test that security headers are present on all endpoints"""
+        # Test health endpoint
+        response = client.get("/health")
+        assert "X-Frame-Options" in response.headers
+        assert "X-Content-Type-Options" in response.headers
+
+        # Test root endpoint
+        response = client.get("/")
+        assert "X-Frame-Options" in response.headers
+        assert "X-Content-Type-Options" in response.headers
+
+    def test_security_headers_on_404(self, client):
+        """Test that security headers are present even on 404 responses"""
+        response = client.get("/nonexistent-endpoint")
+        assert response.status_code == 404
+        assert "X-Frame-Options" in response.headers
+        assert "X-Content-Type-Options" in response.headers
+        assert "X-XSS-Protection" in response.headers