Most, if not all, GUI applications that are developed have to be supplemented with dialogs and widgets to enable different use cases and workflows for the user. Dialogs are usually small-sized windows with specific functionalities that aid the users with selecting or executing some operation. The most common examples of dialogs include the File Open dialog in many text and image editing applications, the Color Chooser dialog in various paint applications, and so on. In many GUI toolkits, the terms dialogs and widgets are used interchangeably. As a general difference, dialogs are the small windows whose main purpose is to establish a connection between the user and the program. We normally use dialog boxes to receive an input from the users or to represent an output or error message to the users. However, widgets are collections of the building blocks of the applications, such as buttons, check boxes, progress bars, and so on. This chapter will introduce you...