The Option key is a modifier key present on Apple keyboards. It is located between the Control key and Command key on a typical Mac keyboard. There are two option keys on modern Mac desktop and notebook keyboards, one on each side of the space bar.

Apple commonly uses the symbol ⌥ (U+2325, "OPTION KEY") to represent the Option key. From 1980 to 1984, on the Apple II family, this key was known as the closed apple key, and had a black line drawing of a filled-in apple on it. (See command key for information about the history and the "open apple".)

Since the 1990s, "alt" typically appears on the key, as well, for use as an Alt key with non-Mac software, such as Unix and Windows programs. However, the Option key in a Mac operating system functions differently from the Alt key under other Unix-like systems or Microsoft Windows. Most notably, it is not used to access menus or hotkeys, but is instead used as a modifier for other command codes, and also to provide easier access to various accents and symbols. In this regard, it is akin to the AltGr key, found on some IBM-compatible PC keyboards.