The sailfish is one of two species of marine fish in the genus Istiophorus, which belong to the family Istiophoridae (marlins). They are predominantly blue to gray in colour and have a characteristically large dorsal fin known as the sail, which often stretches the entire length of the back. Another notable characteristic is the elongated rostrum (bill) consistent with that of other marlins and the swordfish, which together constitute what are known as billfish in sport fishing circles. Sailfish live in colder pelagic waters of all Earth's oceans, and hold the record for the highest speed of any marine animal.

Marlins are fish from the family Istiophoridae, which includes 11 species.