In computing, a checkbox (check box, tickbox, or tick box) is a graphical user interface element (widget) that permits the user to make multiple selections from a number of options (contrary to a radio button where only one choice is possible) or to have the user answer yes (checked) or no (not checked) on a simple yes/no question.

Normally, checkboxes are shown on the screen as a square box that can contain white space (for false) or a tick mark or X (for true), as pictured. A caption describing the meaning of the checkbox is normally shown adjacent to the checkbox. Inverting the state of a checkbox is done by clicking the mouse on the box, or the caption, or by using a keyboard shortcut, such as the space bar.

Some applications use checkboxes that allow an indeterminate state in addition to the two provided by a normal checkbox. This third state is shown as a square or dash in the checkbox, and indicates that its state is neither checked nor unchecked. This is most often used when the checkbox is tied to a collection of items in mixed states. The indeterminate state cannot usually be selected by the user, and switches to a checked state when activated.