The species have a worldwide distribution in temperate and tropical seas, mostly between about 43° N and S latitude, but to 60° N in the warm waters of the North Atlantic Current in the eastern North Atlantic Ocean; they do not occur in colder arctic or antarctic waters.

Several of the species are abundant and well-known birds in their ranges; one is however extremely rare and critically endangered.

[5] The type species was subsequently designated as the sandwich tern (Thalasseus sandvicensis).

[7] The genus contains eight species:[8] An early Pliocene fossil bone fragment from the northeastern United States closely resembles a modern royal tern.

It may be an unexpectedly early (3.7–4.8 million years before present) specimen of that species, or an ancestral member of the crested tern group.