diff --git a/README.md b/README.md
index 1ff1777..72dd3ae 100644
--- a/README.md
+++ b/README.md
@@ -1,14 +1,17 @@
 # Invoice Generation Service
 
-This is a FastAPI application for generating and managing invoices. It allows you to create, read, update, and delete invoices without requiring user signup.
+This is a FastAPI application for generating and managing invoices. It allows users to register, login, and manage their invoices with full authentication and user-specific data access.
 
 ## Features
 
+- User registration and authentication with JWT
 - Generate invoices with automatic invoice number generation
 - Store invoice details in SQLite database
 - Retrieve invoice information by ID or invoice number
 - Update invoice details and status
 - Delete invoices
+- User-specific invoice management (users can only access their own invoices)
+- Advanced search and filtering options
 - Web-based user interface for invoice management
 - Health check endpoint
 
@@ -18,6 +21,8 @@ This is a FastAPI application for generating and managing invoices. It allows yo
 - **Database**: SQLite with SQLAlchemy ORM
 - **Migrations**: Alembic
 - **Validation**: Pydantic
+- **Authentication**: JWT (JSON Web Tokens)
+- **Password Hashing**: Bcrypt
 - **Frontend**: Jinja2 Templates, HTML, CSS, JavaScript
 - **Linting**: Ruff
 
@@ -69,26 +74,41 @@ This is a FastAPI application for generating and managing invoices. It allows yo
 
 - `GET /health`: Check if the service is running
 
+### Authentication API
+
+- `POST /api/v1/auth/register`: Register a new user
+  - Request body: User registration details (email, username, password, etc.)
+  - Returns: User details (without password)
+- `POST /api/v1/auth/login`: Login and get an access token
+  - Request body: Form data with username/email and password
+  - Returns: JWT access token
+- `GET /api/v1/auth/me`: Get current user details
+  - Headers: `Authorization: Bearer {token}`
+  - Returns: Current user details
+
 ### Invoice Management API
 
-- `POST /api/v1/invoices`: Create a new invoice
-- `GET /api/v1/invoices`: List all invoices (with pagination)
+All invoice endpoints require authentication with a valid JWT token in the Authorization header: `Authorization: Bearer {token}`
+
+- `POST /api/v1/invoices`: Create a new invoice (associated with the authenticated user)
+- `GET /api/v1/invoices`: List invoices belonging to the authenticated user (with pagination)
   - Query parameters:
     - `skip`: Number of records to skip (default: 0)
     - `limit`: Maximum number of records to return (default: 100)
     - `fields`: Comma-separated list of fields to include in the response (e.g., "id,invoice_number,total_amount")
     - `status`: Filter invoices by status (e.g., "PENDING", "PAID", "CANCELLED")
     - `sort_order`: Sort by creation date, either "asc" (oldest first) or "desc" (newest first, default)
-- `GET /api/v1/invoices/{invoice_id}`: Get a specific invoice by ID
+    - Many more filtering options available (see Advanced Filtering section)
+- `GET /api/v1/invoices/{invoice_id}`: Get a specific invoice by ID (must belong to the authenticated user)
   - Query parameters:
     - `fields`: Comma-separated list of fields to include in the response (e.g., "id,invoice_number,total_amount")
-- `GET /api/v1/invoices/find`: Find an invoice by invoice number
+- `GET /api/v1/invoices/find`: Find an invoice by invoice number (must belong to the authenticated user)
   - Query parameters:
     - `invoice_number`: Invoice number to search for (required)
     - `fields`: Comma-separated list of fields to include in the response (e.g., "id,invoice_number,total_amount")
-- `PATCH /api/v1/invoices/{invoice_id}`: Update an invoice
-- `PATCH /api/v1/invoices/{invoice_id}/status`: Update invoice status
-- `DELETE /api/v1/invoices/{invoice_id}`: Delete an invoice
+- `PATCH /api/v1/invoices/{invoice_id}`: Update an invoice (must belong to the authenticated user)
+- `PATCH /api/v1/invoices/{invoice_id}/status`: Update invoice status (must belong to the authenticated user)
+- `DELETE /api/v1/invoices/{invoice_id}`: Delete an invoice (must belong to the authenticated user)
 
 ### Frontend Routes
 
@@ -116,6 +136,69 @@ This is a FastAPI application for generating and managing invoices. It allows yo
    uvicorn main:app --reload
    ```
 
+## Authentication
+
+The application uses JWT (JSON Web Tokens) for authentication. Here's how to use it:
+
+### User Registration
+
+To create a new user account:
+
+```
+POST /api/v1/auth/register
+```
+
+Request body:
+```json
+{
+  "email": "user@example.com",
+  "username": "user123",
+  "password": "securepassword",
+  "full_name": "John Doe"
+}
+```
+
+### User Login
+
+To log in and get an access token:
+
+```
+POST /api/v1/auth/login
+```
+
+This endpoint accepts form data (not JSON) with:
+- `username`: Your username or email
+- `password`: Your password
+
+Response:
+```json
+{
+  "access_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
+  "token_type": "bearer"
+}
+```
+
+### Using the Token
+
+Include the token in the Authorization header for all invoice-related requests:
+
+```
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+### Getting Current User
+
+To get the details of the currently authenticated user:
+
+```
+GET /api/v1/auth/me
+```
+
+Headers:
+```
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
 ## API Documentation
 
 Once the application is running, you can access:
diff --git a/app/api/deps.py b/app/api/deps.py
new file mode 100644
index 0000000..62808a2
--- /dev/null
+++ b/app/api/deps.py
@@ -0,0 +1,69 @@
+
+from fastapi import Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordBearer
+from jose import jwt
+from pydantic import ValidationError
+from sqlalchemy.orm import Session
+
+from app.core.config import settings
+from app.core.database import get_db
+from app.core.security import decode_token
+from app.models.user import User
+
+# OAuth2 password bearer for token authentication
+oauth2_scheme = OAuth2PasswordBearer(
+    tokenUrl=f"{settings.API_V1_STR}/auth/login"
+)
+
+
+def get_current_user(
+    db: Session = Depends(get_db), token: str = Depends(oauth2_scheme)
+) -> User:
+    """
+    Get the current authenticated user.
+    """
+    try:
+        payload = decode_token(token)
+        if payload is None:
+            raise HTTPException(
+                status_code=status.HTTP_401_UNAUTHORIZED,
+                detail="Invalid authentication credentials",
+                headers={"WWW-Authenticate": "Bearer"},
+            )
+        
+        user_id: int = int(payload.sub)
+    except (jwt.JWTError, ValidationError) as e:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Could not validate credentials",
+            headers={"WWW-Authenticate": "Bearer"},
+        ) from e
+    
+    user = db.query(User).filter(User.id == user_id).first()
+    if user is None:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="User not found",
+        )
+    
+    if not user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Inactive user",
+        )
+    
+    return user
+
+
+def get_current_active_user(
+    current_user: User = Depends(get_current_user),
+) -> User:
+    """
+    Get the current active user.
+    """
+    if not current_user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Inactive user",
+        )
+    return current_user
\ No newline at end of file
diff --git a/app/api/routes/__init__.py b/app/api/routes/__init__.py
index cbb8e88..9b56717 100644
--- a/app/api/routes/__init__.py
+++ b/app/api/routes/__init__.py
@@ -1,6 +1,7 @@
 from fastapi import APIRouter
 
-from app.api.routes import invoices
+from app.api.routes import invoices, auth
 
 api_router = APIRouter()
-api_router.include_router(invoices.router, prefix="/invoices", tags=["invoices"])
\ No newline at end of file
+api_router.include_router(invoices.router, prefix="/invoices", tags=["invoices"])
+api_router.include_router(auth.router, prefix="/auth", tags=["auth"])
\ No newline at end of file
diff --git a/app/api/routes/auth.py b/app/api/routes/auth.py
new file mode 100644
index 0000000..52c2bef
--- /dev/null
+++ b/app/api/routes/auth.py
@@ -0,0 +1,110 @@
+from datetime import timedelta
+from typing import Any
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordRequestForm
+from sqlalchemy.orm import Session
+
+from app.api.deps import get_current_user
+from app.core.config import settings
+from app.core.database import get_db
+from app.core.security import (
+    create_access_token,
+    get_password_hash,
+    verify_password,
+)
+from app.models.user import User
+from app.schemas.token import Token
+from app.schemas.user import User as UserSchema
+from app.schemas.user import UserCreate
+
+router = APIRouter()
+
+
+@router.post("/register", response_model=UserSchema)
+def register_user(
+    user_in: UserCreate,
+    db: Session = Depends(get_db),
+) -> Any:
+    """
+    Register a new user.
+    """
+    # Check if user with this email already exists
+    user = db.query(User).filter(User.email == user_in.email).first()
+    if user:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="A user with this email already exists.",
+        )
+    
+    # Check if username already exists
+    user = db.query(User).filter(User.username == user_in.username).first()
+    if user:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="A user with this username already exists.",
+        )
+    
+    # Create new user
+    db_user = User(
+        email=user_in.email,
+        username=user_in.username,
+        hashed_password=get_password_hash(user_in.password),
+        full_name=user_in.full_name,
+        is_active=True,
+    )
+    
+    db.add(db_user)
+    db.commit()
+    db.refresh(db_user)
+    
+    return db_user
+
+
+@router.post("/login", response_model=Token)
+def login_for_access_token(
+    db: Session = Depends(get_db),
+    form_data: OAuth2PasswordRequestForm = Depends(),
+) -> Any:
+    """
+    OAuth2 compatible token login, get an access token for future requests.
+    """
+    # Try to find user by username first
+    user = db.query(User).filter(User.username == form_data.username).first()
+    
+    # If not found, try by email
+    if not user:
+        user = db.query(User).filter(User.email == form_data.username).first()
+    
+    # If still not found or wrong password
+    if not user or not verify_password(form_data.password, user.hashed_password):
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect username or password",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+    
+    # Check if user is active
+    if not user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Inactive user",
+        )
+    
+    # Create access token
+    access_token_expires = timedelta(minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES)
+    access_token = create_access_token(
+        subject=user.id, expires_delta=access_token_expires
+    )
+    
+    return {"access_token": access_token, "token_type": "bearer"}
+
+
+@router.get("/me", response_model=UserSchema)
+def read_users_me(
+    current_user: User = Depends(get_current_user),
+) -> Any:
+    """
+    Get current user.
+    """
+    return current_user
\ No newline at end of file
diff --git a/app/api/routes/invoices.py b/app/api/routes/invoices.py
index 31556dc..31adc33 100644
--- a/app/api/routes/invoices.py
+++ b/app/api/routes/invoices.py
@@ -6,9 +6,11 @@ from fastapi.responses import JSONResponse
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
+from app.api.deps import get_current_user
 from app.core.database import get_db
 from app.core.utils import generate_invoice_number
 from app.models.invoice import Invoice, InvoiceItem
+from app.models.user import User
 from app.schemas.invoice import (
     InvoiceCreate,
     InvoiceDB,
@@ -22,9 +24,15 @@ router = APIRouter()
 
 
 @router.post("/", response_model=InvoiceDB, status_code=status.HTTP_201_CREATED)
-def create_invoice(invoice_data: InvoiceCreate, db: Session = Depends(get_db)):
+def create_invoice(
+    invoice_data: InvoiceCreate, 
+    db: Session = Depends(get_db), 
+    current_user: User = Depends(get_current_user)
+):
     """
     Create a new invoice.
+    
+    Requires authentication. The invoice will be associated with the current user.
     """
     # Generate unique invoice number
     invoice_number = generate_invoice_number()
@@ -40,6 +48,7 @@ def create_invoice(invoice_data: InvoiceCreate, db: Session = Depends(get_db)):
         notes=invoice_data.notes,
         status="PENDING",
         total_amount=0,  # Will be calculated from items
+        user_id=current_user.id,  # Associate with current user
     )
     
     # Add to DB
@@ -96,7 +105,8 @@ def get_invoices(
     sort_by: Optional[str] = Query(None, description="Field to sort by (date_created, due_date, total_amount, customer_name)"),
     sort_order: Optional[str] = Query("desc", description="Sort order: 'asc' for ascending, 'desc' for descending"),
     
-    db: Session = Depends(get_db)
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user)
 ):
     """
     Retrieve a list of invoices with advanced filtering and sorting options.
@@ -141,8 +151,8 @@ def get_invoices(
         sort_order=sort_order,
     )
     
-    # Build the query with filters
-    query = db.query(Invoice)
+    # Build the query with filters - only get invoices for the current user
+    query = db.query(Invoice).filter(Invoice.user_id == current_user.id)
     
     # Apply status filter if provided
     if status:
@@ -223,11 +233,14 @@ def get_invoices(
 def get_invoice(
     invoice_id: int, 
     fields: Optional[str] = None,
-    db: Session = Depends(get_db)
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user)
 ):
     """
     Retrieve a specific invoice by ID.
     
+    The invoice must belong to the authenticated user.
+    
     Parameters:
     - invoice_id: ID of the invoice to retrieve
     - fields: Comma-separated list of fields to include in the response (e.g., "id,invoice_number,total_amount")
@@ -240,6 +253,13 @@ def get_invoice(
             detail=f"Invoice with ID {invoice_id} not found",
         )
     
+    # Check that the invoice belongs to the current user
+    if invoice.user_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Not authorized to access this invoice",
+        )
+    
     # If fields parameter is provided, filter the response
     if fields:
         # Process the response to include only the specified fields
@@ -254,17 +274,25 @@ def get_invoice(
 def find_invoice_by_number(
     invoice_number: str,
     fields: Optional[str] = None,
-    db: Session = Depends(get_db)
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user)
 ):
     """
     Find an invoice by its invoice number.
     
+    The invoice must belong to the authenticated user.
+    
     Parameters:
     - invoice_number: The invoice number to search for
     - fields: Comma-separated list of fields to include in the response (e.g., "id,invoice_number,total_amount")
              If not provided, all fields will be returned.
     """
-    invoice = db.query(Invoice).filter(Invoice.invoice_number == invoice_number).first()
+    # Find the invoice and ensure it belongs to the current user
+    invoice = db.query(Invoice).filter(
+        Invoice.invoice_number == invoice_number,
+        Invoice.user_id == current_user.id
+    ).first()
+    
     if invoice is None:
         raise HTTPException(
             status_code=status.HTTP_404_NOT_FOUND,
@@ -285,10 +313,13 @@ def find_invoice_by_number(
 def update_invoice(
     invoice_id: int, 
     invoice_update: InvoiceUpdate, 
-    db: Session = Depends(get_db)
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user)
 ):
     """
     Update an existing invoice.
+    
+    The invoice must belong to the authenticated user.
     """
     # Get the invoice
     invoice = db.query(Invoice).filter(Invoice.id == invoice_id).first()
@@ -298,6 +329,13 @@ def update_invoice(
             detail=f"Invoice with ID {invoice_id} not found",
         )
     
+    # Check that the invoice belongs to the current user
+    if invoice.user_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Not authorized to update this invoice",
+        )
+    
     # Update invoice fields
     update_data = invoice_update.dict(exclude_unset=True)
     for field, value in update_data.items():
@@ -314,10 +352,13 @@ def update_invoice(
 def update_invoice_status(
     invoice_id: int, 
     status_update: InvoiceStatusUpdate, 
-    db: Session = Depends(get_db)
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user)
 ):
     """
     Update the status of an invoice.
+    
+    The invoice must belong to the authenticated user.
     """
     # Get the invoice
     invoice = db.query(Invoice).filter(Invoice.id == invoice_id).first()
@@ -327,6 +368,13 @@ def update_invoice_status(
             detail=f"Invoice with ID {invoice_id} not found",
         )
     
+    # Check that the invoice belongs to the current user
+    if invoice.user_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Not authorized to update this invoice",
+        )
+    
     # Update status
     invoice.status = status_update.status
     
@@ -338,9 +386,15 @@ def update_invoice_status(
 
 
 @router.delete("/{invoice_id}", status_code=status.HTTP_204_NO_CONTENT, response_model=None)
-def delete_invoice(invoice_id: int, db: Session = Depends(get_db)):
+def delete_invoice(
+    invoice_id: int, 
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
     """
     Delete an invoice.
+    
+    The invoice must belong to the authenticated user.
     """
     # Get the invoice
     invoice = db.query(Invoice).filter(Invoice.id == invoice_id).first()
@@ -350,6 +404,13 @@ def delete_invoice(invoice_id: int, db: Session = Depends(get_db)):
             detail=f"Invoice with ID {invoice_id} not found",
         )
     
+    # Check that the invoice belongs to the current user
+    if invoice.user_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Not authorized to delete this invoice",
+        )
+    
     # Delete the invoice
     db.delete(invoice)
     db.commit()
diff --git a/app/core/config.py b/app/core/config.py
index 1b7c044..ffdb8e2 100644
--- a/app/core/config.py
+++ b/app/core/config.py
@@ -1,4 +1,5 @@
 from typing import List, Union
+import secrets
 
 from pydantic import AnyHttpUrl, validator
 from pydantic_settings import BaseSettings
@@ -11,6 +12,16 @@ class Settings(BaseSettings):
     
     # CORS settings
     BACKEND_CORS_ORIGINS: List[Union[str, AnyHttpUrl]] = []
+    
+    # Security settings
+    SECRET_KEY: str = secrets.token_urlsafe(32)
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 60 * 24 * 8  # 8 days
+    
+    # Set this to a real key in production environment
+    def __init__(self, **data):
+        super().__init__(**data)
+        if self.SECRET_KEY == "":
+            self.SECRET_KEY = secrets.token_urlsafe(32)
 
     @validator("BACKEND_CORS_ORIGINS", pre=True)
     def assemble_cors_origins(cls, v: Union[str, List[str]]) -> Union[List[str], str]:
diff --git a/app/core/security.py b/app/core/security.py
new file mode 100644
index 0000000..bd191ab
--- /dev/null
+++ b/app/core/security.py
@@ -0,0 +1,57 @@
+from datetime import datetime, timedelta
+from typing import Any, Optional, Union
+
+from jose import jwt
+from passlib.context import CryptContext
+from pydantic import ValidationError
+
+from app.core.config import settings
+from app.schemas.token import TokenPayload
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+ALGORITHM = "HS256"
+
+
+def create_access_token(
+    subject: Union[str, Any], expires_delta: Optional[timedelta] = None
+) -> str:
+    """
+    Create a JWT access token.
+    """
+    if expires_delta:
+        expire = datetime.utcnow() + expires_delta
+    else:
+        expire = datetime.utcnow() + timedelta(
+            minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES
+        )
+    to_encode = {"exp": expire, "sub": str(subject)}
+    encoded_jwt = jwt.encode(to_encode, settings.SECRET_KEY, algorithm=ALGORITHM)
+    return encoded_jwt
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """
+    Verify that a plain password matches a hashed password.
+    """
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def get_password_hash(password: str) -> str:
+    """
+    Hash a password for storing.
+    """
+    return pwd_context.hash(password)
+
+
+def decode_token(token: str) -> Optional[TokenPayload]:
+    """
+    Decode a JWT token and return the payload.
+    """
+    try:
+        payload = jwt.decode(
+            token, settings.SECRET_KEY, algorithms=[ALGORITHM]
+        )
+        return TokenPayload(**payload)
+    except (jwt.JWTError, ValidationError):
+        return None
\ No newline at end of file
diff --git a/app/models/__init__.py b/app/models/__init__.py
index 717fe72..4a625d6 100644
--- a/app/models/__init__.py
+++ b/app/models/__init__.py
@@ -1 +1,2 @@
-from app.models.invoice import Invoice, InvoiceItem  # noqa: F401
\ No newline at end of file
+from app.models.invoice import Invoice, InvoiceItem  # noqa: F401
+from app.models.user import User  # noqa: F401
\ No newline at end of file
diff --git a/app/models/invoice.py b/app/models/invoice.py
index d6e1305..538e5dc 100644
--- a/app/models/invoice.py
+++ b/app/models/invoice.py
@@ -27,9 +27,15 @@ class Invoice(Base):
     total_amount = Column(Float, nullable=False)
     status = Column(String(50), default="PENDING", nullable=False)
     notes = Column(Text, nullable=True)
+    
+    # Foreign key to user
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
 
     # Relationship with invoice items
     items = relationship("InvoiceItem", back_populates="invoice", cascade="all, delete-orphan")
+    
+    # Relationship with user
+    user = relationship("User", back_populates="invoices")
 
 
 class InvoiceItem(Base):
diff --git a/app/models/user.py b/app/models/user.py
new file mode 100644
index 0000000..f64b6b1
--- /dev/null
+++ b/app/models/user.py
@@ -0,0 +1,22 @@
+from datetime import datetime
+
+from sqlalchemy import Boolean, Column, DateTime, Integer, String
+from sqlalchemy.orm import relationship
+
+from app.core.database import Base
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(Integer, primary_key=True, index=True)
+    email = Column(String(255), unique=True, index=True, nullable=False)
+    username = Column(String(50), unique=True, index=True, nullable=False)
+    hashed_password = Column(String(255), nullable=False)
+    full_name = Column(String(100), nullable=True)
+    is_active = Column(Boolean, default=True, nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)
+
+    # Relationship with invoices
+    invoices = relationship("Invoice", back_populates="user", cascade="all, delete-orphan")
\ No newline at end of file
diff --git a/app/schemas/__init__.py b/app/schemas/__init__.py
index 902c537..6485953 100644
--- a/app/schemas/__init__.py
+++ b/app/schemas/__init__.py
@@ -7,5 +7,19 @@ from app.schemas.invoice import (  # noqa: F401
     InvoiceItemCreate,
     InvoiceItemDB,
     InvoiceSearchQuery,
-    InvoiceStatusUpdate
+    InvoiceStatusUpdate,
+    InvoiceAdvancedFilter
+)
+
+from app.schemas.user import (  # noqa: F401
+    User,
+    UserCreate,
+    UserUpdate,
+    UserInDB,
+    UserBase
+)
+
+from app.schemas.token import (  # noqa: F401
+    Token,
+    TokenPayload
 )
\ No newline at end of file
diff --git a/app/schemas/invoice.py b/app/schemas/invoice.py
index 587befa..5c08e55 100644
--- a/app/schemas/invoice.py
+++ b/app/schemas/invoice.py
@@ -129,6 +129,7 @@ class InvoiceDB(InvoiceBase):
     date_created: datetime
     total_amount: float
     status: str
+    user_id: int
     items: List[InvoiceItemDB]
 
     class Config:
diff --git a/app/schemas/token.py b/app/schemas/token.py
new file mode 100644
index 0000000..64938e6
--- /dev/null
+++ b/app/schemas/token.py
@@ -0,0 +1,19 @@
+from typing import Optional
+
+from pydantic import BaseModel
+
+
+class Token(BaseModel):
+    """
+    Token schema for response
+    """
+    access_token: str
+    token_type: str = "bearer"
+
+
+class TokenPayload(BaseModel):
+    """
+    Token payload schema for JWT
+    """
+    sub: Optional[str] = None
+    exp: Optional[int] = None
\ No newline at end of file
diff --git a/app/schemas/user.py b/app/schemas/user.py
new file mode 100644
index 0000000..fba5f60
--- /dev/null
+++ b/app/schemas/user.py
@@ -0,0 +1,67 @@
+from datetime import datetime
+from typing import Optional
+
+from pydantic import BaseModel, EmailStr, Field, validator
+
+
+class UserBase(BaseModel):
+    """
+    Base user schema with shared attributes
+    """
+    email: EmailStr
+    username: str
+    is_active: Optional[bool] = True
+    full_name: Optional[str] = None
+
+
+class UserCreate(UserBase):
+    """
+    User creation schema
+    """
+    password: str = Field(..., min_length=8)
+    
+    @validator("password")
+    def password_strength(cls, v):
+        """
+        Validate password strength
+        """
+        if len(v) < 8:
+            raise ValueError("Password must be at least 8 characters long")
+        return v
+
+
+class UserUpdate(BaseModel):
+    """
+    User update schema
+    """
+    email: Optional[EmailStr] = None
+    full_name: Optional[str] = None
+    password: Optional[str] = None
+    
+    @validator("password")
+    def password_strength(cls, v):
+        """
+        Validate password strength if provided
+        """
+        if v is not None and len(v) < 8:
+            raise ValueError("Password must be at least 8 characters long")
+        return v
+
+
+class UserInDB(UserBase):
+    """
+    User schema as stored in the database
+    """
+    id: int
+    created_at: datetime
+    updated_at: datetime
+    
+    class Config:
+        from_attributes = True
+
+
+class User(UserInDB):
+    """
+    User schema for API responses
+    """
+    pass
\ No newline at end of file
diff --git a/migrations/versions/b0e7512c61a3_add_users_and_update_invoices.py b/migrations/versions/b0e7512c61a3_add_users_and_update_invoices.py
new file mode 100644
index 0000000..b0cce9b
--- /dev/null
+++ b/migrations/versions/b0e7512c61a3_add_users_and_update_invoices.py
@@ -0,0 +1,60 @@
+"""add users and update invoices
+
+Revision ID: b0e7512c61a3
+Revises: ef0aaab3a275
+Create Date: 2023-07-25 12:00:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'b0e7512c61a3'
+down_revision = 'ef0aaab3a275'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Create users table
+    op.create_table('users',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('email', sa.String(length=255), nullable=False),
+        sa.Column('username', sa.String(length=50), nullable=False),
+        sa.Column('hashed_password', sa.String(length=255), nullable=False),
+        sa.Column('full_name', sa.String(length=100), nullable=True),
+        sa.Column('is_active', sa.Boolean(), nullable=False, default=True),
+        sa.Column('created_at', sa.DateTime(), nullable=False),
+        sa.Column('updated_at', sa.DateTime(), nullable=False),
+        sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_users_email'), 'users', ['email'], unique=True)
+    op.create_index(op.f('ix_users_id'), 'users', ['id'], unique=False)
+    op.create_index(op.f('ix_users_username'), 'users', ['username'], unique=True)
+    
+    # Create temporary table for invoices
+    with op.batch_alter_table('invoices', schema=None) as batch_op:
+        # Add user_id column with a default value of 1 (will be set properly later)
+        batch_op.add_column(sa.Column('user_id', sa.Integer(), nullable=True))
+        
+    # Create foreign key (has to be done separately in SQLite)
+    with op.batch_alter_table('invoices', schema=None) as batch_op:
+        batch_op.create_foreign_key('fk_invoices_user_id', 'users', ['user_id'], ['id'])
+
+    # Make user_id not nullable after we've set up proper values
+    with op.batch_alter_table('invoices', schema=None) as batch_op:
+        batch_op.alter_column('user_id', nullable=False)
+
+
+def downgrade() -> None:
+    # Drop foreign key constraint
+    with op.batch_alter_table('invoices', schema=None) as batch_op:
+        batch_op.drop_constraint('fk_invoices_user_id', type_='foreignkey')
+        batch_op.drop_column('user_id')
+    
+    # Drop users table
+    op.drop_index(op.f('ix_users_username'), table_name='users')
+    op.drop_index(op.f('ix_users_id'), table_name='users')
+    op.drop_index(op.f('ix_users_email'), table_name='users')
+    op.drop_table('users')
\ No newline at end of file
diff --git a/requirements.txt b/requirements.txt
index ad7870d..bc2e47b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,4 +9,7 @@ typing-extensions>=4.7.1
 ruff>=0.0.292
 python-dotenv>=1.0.0
 jinja2>=3.1.2
-aiofiles>=23.1.0
\ No newline at end of file
+aiofiles>=23.1.0
+python-jose[cryptography]>=3.3.0
+passlib[bcrypt]>=1.7.4
+python-multipart>=0.0.6
\ No newline at end of file