AltGr (also Alt Graph, Alt Graphic, Alt Graphics, Alt Grill, Alt Car or Alt Char) is a modifier key found on many computer keyboards and primarily used to type characters that are unusual for the locale of the keyboard layout, such as currency symbols and accented letters. On a typical IBM compatible PC keyboard, the AltGr key, when present, takes the place of the right-hand Alt key. In Mac OS X, the Option key has functions similar to the AltGr key.

AltGr is used similarly to the Shift key: it is held down when another key is struck in order to obtain a character other than the one that the latter normally produces. AltGr and Shift can also sometimes be combined to obtain yet another character. For example, on the US-International keyboard layout, the C key can be used to insert four different characters:

The meaning of the key's abbreviation is not explicitly given in many IBM PC compatible technical reference manuals.^{[citation needed]} However, IBM states that AltGr is an abbreviation for alternate graphic, and Sun keyboards label the key as Alt Graph.