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

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