One or more buttons on a computer mouse. Different computer systems and different manufacturers make mice with varying number of buttons, each configuration altering the way objects can be selected and features activated. The simplest configuration is the Macintosh mouse, which has but one button with which all clicking and double-clicking is performed. The Microsoft Mouse has two buttons, while the Mouse Systems Mouse has three. Some mice have more than three buttons. Usually, the extra buttons can be programmed by the user to control specific functions.