This article does not cite any references or sources. (January 2008) Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.

Num Lock is a key on the numeric keypad of most computer keyboards, used to switch that pad between number entry and arrow keys. It is a toggle key, like Caps Lock and Scroll Lock. Its state is commonly represented by an LED light built into the keyboard.

The Num Lock key exists because earlier 84-key IBM PC keyboards did not have arrows separate from the numeric keypad. Num Lock would be used to choose between the two functions. On laptop computers, Num Lock keys are used to convert part of the main keyboard to act as a (slightly skewed) numeric keypad rather than letters.

These days since many computers have a full-size keyboard, Num Lock is rarely used for its original purpose, and ends up confusing the user if the computer has for some reason activated or deactivated the Num Lock key without the user being aware of it.

Num Lock is also used in standard BIOS for extra input.