Initialization messages are sent by Windows when an application creates a menu or dialog box. The following list briefly describes each initialization message:
| Message | Description | |
| WM_INITDIALOG | Sent immediately before a dialog box is displayed. | |
| WM_INITMENU | Requests that a menu be initialized. | |
| WM_INITMENUPOPUP | Sent immediately before a pop-up menu is displayed. |