In user interface design, a mode is a distinct setting within a computer program or any physical machine interface, in which the same user input will produce different results than it would in other settings.

The most well-known modal interface components are probably the Caps lock and Insert keys on the standard computer keyboard, both of which put the user's typing into a different mode after being pressed, then return it to the regular mode after being re-pressed.

There are several popular examples of software employing modes:

• vi - has one mode for inserting text, and a separate mode for entering commands. Some people also call vi's ability to line-edit a "mode" (even though it is launched outside of vi's normal interface, by invoking "ex" from the operating system's command line interface.)
• Emacs - has many modes that can be evoked based on file type to more easily edit files of a certain type. Modes are written in Emacs's LISP, and all modes may not be included with all versions.
• Cisco IOS - in order to execute certain commands, you must enter a certain "command mode" that allows you to execute that command.
• Also, tool palettes in photo-editing and drawing applications are classical examples of a modal interface.

Modes are generally frowned upon in interface design because they inevitably lead to input errors, known as mode errors, when the user forgets what state the interface is in. Interface guru Jef Raskin, in his book "The Humane Interface", came out strongly against modes, writing, "Modes are a significant source of errors, confusion, unnecessary restrictions, and complexity in interfaces." Later he notes, "'It is no accident that swearing is denoted by #&%!#$&,' writes my colleague, Dr. James Winter; it is 'what a typewriter used to do when you typed numbers when the Caps Lock was engaged'."

In the book, Raskin also championed what he termed "quasimodes", which are modes that are kept in place only through some constant action on the part of the user; Shift keys, Alt key and Control keys are all examples of a quasimodal interface.

An interface that uses no modes is known as a modeless interface.

User interface