Also known as Mexican lime and West Indies lime. Cultivated for thousands of years in the Indo-Malayan region, It made its way to North Africa and the Near East via Arabian traders, and then carried on to Palestine and Mediterranean Europe by the Crusaders. Columbus is credited with bringing the Key lime to Hispaniola, where it was carried on by Spanish settlers to Florida.  It flourished in South Florida, particularly the Florida Keys.

Key limes are much smaller than Persian limes, nearly spherical, thin-skinned, and often contain a few seeds. Green key limes are actually immature fruits, prized for their acidity. As they ripen to a yellow color, the acid content diminishes greatly, resulting in a sweeter fruit.