Pen computing refers to any computer user-interface using a digital pen or stylus and tablet, over input devices such as a keyboard or a mouse.

Historically, pen computing (defined as a computer system employing a user-interface using a pointing device plus handwriting recognition as the primary means for interactive user input) predates the use of a mouse and graphical display by at least two decades, starting with the Stylator and RAND Tablet systems of the 1950s and early 1960s.

User interfaces for pen computing can be implemented in several ways. Current systems generally employ a combination of these techniques.

The tablet and stylus are used as pointing devices, such as to replace a mouse. While a mouse is a relative pointing device (one uses the mouse to "push the cursor around" on a screen), a tablet is an absolute pointing device (one places the stylus where the cursor is to appear).

There are a number of human factors to be considered when actually substituting a stylus and tablet for a mouse. For example, it is much harder to target or tap the same exact position twice with a stylus, so "double-tap" operations with a stylus are harder to perform if the system is expecting "double-click" input from a mouse.

A finger can be used as the stylus on a touch-sensitive tablet surface, such as with a touchscreen.

The tablet and stylus can be used to replace a keyboard, or both a mouse and a keyboard, by using the tablet and stylus in two modes:

Different systems switch between the modes (pointing vs. handwriting recognition) by different means, e.g.