The circumstances concerning the diffusion of the main cultivated citrus from their places of origin in Asia are studied here, showing that the citron (Citrus medica L.) was the only one knew in Ancient times in Europe, while the lemon (C. limon [L.] Osbeck), lime (C. aurantiifolia [Christm.] Swingle), pomelo (C. maxima [Burm.] Merr.) and sour orange (C. × aurantium L.) were introduced to Europe by the Muslims via the Iberian Peninsula and Sicily, and that the grapefruit (C. paradisi Macfad.), mandarin (C. reticulata Blanco) and sweet orange (C. × aurantium L.) arrived to the West between the fifteenth and nineteenth centuries as a result of the trade with the British and Portuguese colonies.