Dialog windows can be modal or modeless. A modal dialog window requires that the dialog window be dismissed before the user can activate other windows in the same application. Generally, an application uses a modal dialog window to get essential information from the user before proceeding with an operation. A modeless dialog window allows the user to activate other windows in the same application without dismissing the dialog window. Both modal and modeless dialog windows allow the user to activate windows in another application before responding to the dialog window.

Modal dialog windows are easier for an application to manage because they are created, perform their task, and are closed, all with a single function call.

Modeless dialog windows require more attention from the application because they exist until explicitly dismissed. Modeless dialog windows provide a more flexible interface, however, by allowing the user to move to other windows in the application before responding to the dialog window.