The Caspian tern (Hydroprogne caspia) is a species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic of its genus, and has no accepted subspecies.
Adult birds have black legs, and a long thick red-orange bill with a small black tip. They have a white head with a black cap and white neck, belly, and tail. The upper wings and back are pale grey; the underwings are pale with dark primary feathers. In-flight, the tail is less forked than other terns, and wingtips are black on the underside. In winter, the black cap is still present (unlike many other terns), but with some white streaking on the forehead. The call is a loud heron-like croak.