AltGr is a modifier key found on many computer keyboards. It is primarily used to type special characters and symbols that are not widely used in the territory where sold, such as foreign currency symbols, typographic marks and accented letters. On a typical Windows-compatible PC keyboard, the AltGr key, when present, takes the place of the right-hand Alt key. The key at this location will operate as AltGr if a keyboard layout using AltGr is chosen in the operating system, regardless of what is engraved on the key. In macOS, the Option key has functions similar to the AltGr key.

A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Replacing early punched cards and paper tape technology, interaction via teleprinter-style keyboards have been the main input method for computers since the 1970s, supplemented by the computer mouse since the 1980s.