The Caspian gull (Larus cachinnans) is a large gull and a member of the herring and lesser black-backed gull complex.
The Caspian gull has a long, slender bill, accentuated by the sloping forehead. The legs, wings, and neck are longer than those of the herring gull and yellow-legged gull. The eye is small and often dark, and the legs vary from pale pink to a pale yellowish colour. The back and wings are a slightly darker shade of grey than the herring gull, but slightly paler than the yellow-legged gull. The outermost primary feather has a large white tip and a white tongue running up the inner web.
First-winter birds have a pale head with dark streaking on the back of the neck. The underparts are pale and the back is greyish. The greater and median wing coverts have whitish tips forming two pale lines across the wing.