Sailfish are two species of fish in the genus Istiophorus, living in warmer sections of all the oceans of the world. They are blue to grey in color and have a characteristic erectile dorsal fin known as a sail, which often stretches the entire length of the back. Another notable characteristic is the elongated bill, resembling that of the swordfish and other marlins. They are therefore described as billfish in sport fishing circles.

The sail is normally kept folded down and to the side when swimming, but it may be raised when the sailfish feels threatened or excited, making the fish appear much larger than it actually is. This tactic has also been observed during feeding, when a group of sailfish use their sails to "herd" a school of fish or squid.

Sailfish are highly prized game fish and are known for their incredible jumps. The sailfish can also rapidly turn its body light blue with stripes when excited, confusing its prey and making capture easier, while signalling its intentions to fellow sailfish.