The grapefruit (Citrus × paradisi) is a subtropical citrus tree known for its relatively large sour to semisweet, somewhat bitter fruit. The interior flesh is segmented and varies in colour from pale yellow to dark pink.

Grapefruit is a citrus hybrid originating in Barbados as an accidental cross between the sweet orange (C. sinensis) and the pomelo or shaddock (C. maxima), both of which were introduced from Asia in the 17th century. When found, it was called the forbidden fruit. In the past it was referred to as the pomelo, but that term is now the common name for Citrus maxima.

In 2019, world production of grapefruits (combined with pomelos) was 9.3 million tonnes, of which 53% was in China. Other significant producers include Vietnam, United States and Mexico.

The evergreen grapefruit trees usually grow to around 5–6 m (16–20 ft) tall, although they may reach 13–15 m (43–49 ft). The leaves are glossy, dark green, long (up to 15 cm (5.9 in)), and thin. It produces 5 cm (2 in) white four-petaled flowers. The fruit is yellow-orange skinned and generally, an oblate spheroid in shape; it ranges in diameter from 10 to 15 cm (3.9 to 5.9 in). The flesh is segmented and acidic, varying in color depending on the cultivars, which include white, pink, and red pulps of varying sweetness (generally, the redder varieties are the sweetest). The 1929 U.S. 'Ruby Red' (of the 'Redblush' variety) was the first grapefruit patent.