An application nearly always starts with a frame window to create a composite window (for example, a main window) that consists of the frame window, several frame-control windows, and a client window. The frame controls conform to the Common User Access (CUA) user interface guidelines. The frame window coordinates the actions of the frame controls and client window, enabling the composite window to act as a single unit.

Frame windows have the preregistered public window class WC_FRAME. The frame-window class, like the preregistered control classes, defines the appearance and behavior of the frame window.