The yellowfin tuna (Thunnus albacares) is a species of found in waters of and subtropical worldwide.

Yellowfin is often marketed as ahi, from the ahi, a name also used there for the closely related . The species name, albacares ("white meat") can also lead to confusion: in English, the tuna (Thunnus alalunga) is a different species, while yellowfin is officially designated albacore in and referred to as albacora by Portuguese fishermen.