The Windows API exposes the core set of functionality provided by the Windows operating system for use in applications. Primarily designed for C/C++ development, the Windows API has been the most direct mechanism with which an application can interact with Windows. 

The Windows API comprises the following functional groups: 

 Base Services—Provides access to the core resources of the computer, such as memory, file systems, devices, processes, and threads 

 Common Control Library—A collection of common control windows used throughout the

Windows operating system, providing the distinctive Windows look and feel

Common Dialog Box Library—A collection of dialog boxes used to execute common tasks,

including file opening, saving, and printing  

 Graphics Device Interface (GDI)—Provides the facilities for an application to generate graphically output to displays, printers, and other devices 

Network Services—Provides access to various networking capabilities of the Windows operating system, including RPC and NetBIOS 

User Interface (UI)—Provides the mechanism for managing windows and controls in an application

and input from devices such as the mouse and keyboard 

Windows Shell—The container that organizes and presents the entire Windows UI, including