diff --git a/README.md b/README.md
index 80c05a8..f708101 100644
--- a/README.md
+++ b/README.md
@@ -151,12 +151,13 @@ No user intervention required - complete end-to-end. All configuration and deplo
 
 ## Usage
 
-The CLI has five main commands:
+The CLI has six main commands:
 
 - `devin-cli auth` - Manage authentication
 - `devin-cli create` - Create Devin sessions
 - `devin-cli get` - Get details of existing Devin sessions
 - `devin-cli message` - Send messages to existing Devin sessions
+- `devin-cli upload` - Upload files for use in Devin sessions
 - `devin-cli setup` - Download workflow templates and guides
 
 ### Creating Sessions
@@ -244,6 +245,42 @@ The `message` command:
 - Confirms successful message delivery
 - Returns message ID and session status
 
+### Uploading Files
+
+Use the `upload` command to upload files to Devin for use in session prompts:
+
+```bash
+# Upload a file (displays table format with usage instructions)
+devin-cli upload /path/to/file.py
+
+# Upload and get JSON response
+devin-cli upload /path/to/file.csv --output json
+
+# Upload and display ready-to-use format
+devin-cli upload /path/to/data.json --format-prompt
+```
+
+The `upload` command:
+- Accepts a file path as a required argument
+- Returns the attachment URL from the API
+- Displays instructions on how to use the file in prompts
+- Supports various file types (code, text, CSV, JSON, images, etc.)
+
+**Using uploaded files in session prompts:**
+
+After uploading a file, include it in your session prompt using the ATTACHMENT format:
+
+```bash
+# Create a session with an attached file
+devin-cli create --prompt "Review this code file
+
+ATTACHMENT:\"https://storage.devin.ai/attachments/abc123/file.py\"
+
+Please analyze it for potential bugs."
+```
+
+**Important:** The ATTACHMENT line must be on its own line in the prompt for Devin to recognize it.
+
 ### Setting Up Templates
 
 The `setup` command downloads the latest workflow templates and session guide to your repository:
@@ -306,6 +343,11 @@ For the `devin-cli message` command:
 - `--message, -m`: The message to send (will be prompted if not provided)
 - `--output, -o`: Output format (`json` or `table`, default: `table`)
 
+For the `devin-cli upload` command:
+- `FILE_PATH`: Path to the file to upload (required)
+- `--output, -o`: Output format (`json` or `table`, default: `table`)
+- `--format-prompt`: Display the ready-to-use ATTACHMENT: format
+
 ### Global Options
 
 - `--version`: Show version information
@@ -355,6 +397,19 @@ devin-cli get devin-session-123 --output json     # Get details as JSON
 devin-cli message devin-session-123               # Send message interactively
 devin-cli message devin-session-123 --message "Please continue with the implementation"
 
+# Upload examples
+devin-cli upload requirements.txt              # Upload a file
+devin-cli upload data.csv --output json        # Get JSON output
+devin-cli upload config.json --format-prompt   # Show ready-to-use format
+
+# Combined workflow: upload file and create session
+URL=$(devin-cli upload analysis.py --output json | jq -r '.url')
+devin-cli create --prompt "Review this code
+
+ATTACHMENT:\"$URL\"
+
+Check for security issues."
+
 # Setup examples
 devin-cli setup                   # Download templates to current directory
 devin-cli setup --force          # Overwrite existing files
diff --git a/devin_cli.py b/devin_cli.py
index 6d12cac..792270c 100755
--- a/devin_cli.py
+++ b/devin_cli.py
@@ -166,6 +166,36 @@ def send_message_to_session(session_id: str, payload: dict) -> dict:
         raise DevinAPIError(f"API request failed: {e}")
 
 
+def upload_file(file_path: str) -> str:
+    """Upload a file to Devin attachments API and return the URL"""
+    api_key = get_api_key()
+    
+    if not os.path.exists(file_path):
+        raise DevinAPIError(f"File not found: {file_path}")
+    
+    headers = {
+        'Authorization': f'Bearer {api_key}'
+    }
+    
+    try:
+        with open(file_path, 'rb') as f:
+            files = {'file': f}
+            response = requests.post(
+                'https://api.devin.ai/v1/attachments',
+                headers=headers,
+                files=files,
+                timeout=60
+            )
+            response.raise_for_status()
+            
+            url = response.text.strip()
+            if url.startswith('"') and url.endswith('"'):
+                url = url[1:-1]
+            return url
+    except requests.exceptions.RequestException as e:
+        raise DevinAPIError(f"File upload failed: {e}")
+
+
 def parse_list_input(value: str) -> List[str]:
     """Parse comma-separated string into list"""
     if not value:
@@ -379,6 +409,41 @@ def message(session_id, message, output):
         click.echo(f"❌ Unexpected error: {e}", err=True)
         sys.exit(1)
 
+@cli.command()
+@click.argument('file_path', type=click.Path(exists=True))
+@click.option('--output', '-o', type=click.Choice(['json', 'table']), default='table', help='Output format')
+@click.option('--format-prompt', is_flag=True, help='Output the ready-to-use ATTACHMENT: format')
+def upload(file_path, output, format_prompt):
+    """Upload a file to Devin for use in session prompts"""
+    
+    try:
+        click.echo(f"Uploading file: {file_path}...")
+        url = upload_file(file_path)
+        
+        if output == 'json':
+            result = {'url': url}
+            if format_prompt:
+                result['formatted'] = f'ATTACHMENT:"{url}"'
+            click.echo(json.dumps(result, indent=2))
+        else:
+            click.echo("\n✅ File uploaded successfully!")
+            click.echo(f"URL: {url}")
+            click.echo("\n📋 To use this file in a Devin session prompt, include:")
+            click.echo(f'ATTACHMENT:"{url}"')
+            
+            if format_prompt:
+                click.echo("\n📝 Ready-to-use format:")
+                click.echo(f'ATTACHMENT:"{url}"')
+                
+    except DevinAPIError as e:
+        click.echo(f"❌ Error: {e}", err=True)
+        sys.exit(1)
+    except Exception as e:
+        click.echo(f"❌ Unexpected error: {e}", err=True)
+        sys.exit(1)
+
+
+
 
 @cli.command()
 @click.option('--target-dir', '-t', default='.', help='Target directory to copy files to (default: current directory)')
diff --git a/test_cli.py b/test_cli.py
index 7c87b3f..bd598a8 100644
--- a/test_cli.py
+++ b/test_cli.py
@@ -1031,6 +1031,116 @@ def test_get_and_message_api_error_handling():
     print("✅ API error handling for new commands works correctly")
 
 
+def test_upload_help():
+    """Test upload subcommand help"""
+    print("🧪 Testing upload --help command...")
+    result = run_cli_command(['upload', '--help'])
+    
+    assert result['returncode'] == 0, f"Upload help command failed: {result['stderr']}"
+    assert 'Upload a file to Devin' in result['stdout'], "Upload help text missing"
+    assert '--output' in result['stdout'], "Output option missing from upload help"
+    assert '--format-prompt' in result['stdout'], "Format-prompt option missing from upload help"
+    print("✅ Upload help command works correctly")
+
+
+def test_upload_file_function():
+    """Test upload_file function with mocked API"""
+    print("🧪 Testing upload_file function...")
+    
+    sys.path.insert(0, os.path.dirname(__file__))
+    from devin_cli import upload_file
+    
+    with tempfile.NamedTemporaryFile(mode='w', delete=False, suffix='.txt') as f:
+        f.write("Test content")
+        test_file = f.name
+    
+    try:
+        with patch('devin_cli.requests.post') as mock_post:
+            mock_response = MagicMock()
+            mock_response.status_code = 200
+            mock_response.text = '"https://storage.devin.ai/attachments/test-id/file.txt"'
+            mock_response.raise_for_status = MagicMock()
+            mock_post.return_value = mock_response
+            
+            with patch('devin_cli.get_api_key', return_value='test-key'):
+                url = upload_file(test_file)
+                
+                assert mock_post.call_count == 1, "API should have been called once"
+                call_kwargs = mock_post.call_args[1]
+                assert call_kwargs['headers']['Authorization'] == 'Bearer test-key'
+                assert 'files' in call_kwargs
+                assert call_kwargs['timeout'] == 60
+                
+                assert url == 'https://storage.devin.ai/attachments/test-id/file.txt'
+                assert not url.startswith('"'), "URL should not have quotes"
+                
+        print("✅ Upload file function works correctly")
+    finally:
+        os.unlink(test_file)
+
+
+def test_upload_file_not_found():
+    """Test upload_file with non-existent file"""
+    print("🧪 Testing upload with non-existent file...")
+    
+    sys.path.insert(0, os.path.dirname(__file__))
+    from devin_cli import upload_file, DevinAPIError
+    
+    with patch('devin_cli.get_api_key', return_value='test-key'):
+        try:
+            upload_file('/nonexistent/file.txt')
+            assert False, "Should have raised DevinAPIError"
+        except DevinAPIError as e:
+            assert 'File not found' in str(e)
+    
+    print("✅ File not found error handling works correctly")
+
+
+def test_upload_api_error():
+    """Test upload_file with API error"""
+    print("🧪 Testing upload with API error...")
+    
+    sys.path.insert(0, os.path.dirname(__file__))
+    from devin_cli import upload_file, DevinAPIError
+    
+    with tempfile.NamedTemporaryFile(mode='w', delete=False, suffix='.txt') as f:
+        f.write("Test content")
+        test_file = f.name
+    
+    try:
+        with patch('devin_cli.requests.post') as mock_post:
+            mock_post.side_effect = requests.exceptions.RequestException("API Error")
+            
+            with patch('devin_cli.get_api_key', return_value='test-key'):
+                try:
+                    upload_file(test_file)
+                    assert False, "Should have raised DevinAPIError"
+                except DevinAPIError as e:
+                    assert 'File upload failed' in str(e)
+        
+        print("✅ API error handling works correctly")
+    finally:
+        os.unlink(test_file)
+
+
+def test_upload_command_cli_execution():
+    """Test upload command via CLI"""
+    print("🧪 Testing upload command CLI execution...")
+    
+    with tempfile.NamedTemporaryFile(mode='w', delete=False, suffix='.txt') as f:
+        f.write("Test content for CLI")
+        test_file = f.name
+    
+    try:
+        result = run_cli_command(['upload', '--help'])
+        assert result['returncode'] == 0, "Upload help should work"
+        assert 'Upload a file' in result['stdout']
+        
+        print("✅ Upload command CLI execution works correctly")
+    finally:
+        os.unlink(test_file)
+
+
 def run_all_tests():
     """Run all tests"""
     print("🚀 Starting comprehensive CLI tests...\n")
@@ -1087,6 +1197,12 @@ def run_all_tests():
         # Integration
         test_api_request_structure,
         test_end_to_end_workflow,
+        
+        test_upload_help,
+        test_upload_file_function,
+        test_upload_file_not_found,
+        test_upload_api_error,
+        test_upload_command_cli_execution,
     ]
     
     passed = 0