The Bowhead whale (Balaena mysticetus) is one of four species of marine mammal in the family Balaenidae, part of the order of cetaceans. The bowhead whale is the second largest whale in the world, second only to the blue whale. Bowheads live in icy Arctic seas. To insulate against the cold Arctic waters, bowhead blubber may be 70 centimetres thick and the whales can break through ice of a foot deep to make breathing holes. They were hunted to the brink of extinction during the 1800s, and have been slow to recover. There are likely 20,000 to 40,000 bowheads alive today, living in four or five populations. Amazingly, this whale is known to live to over 100 years of age, a fact established by the discovery of stone harpoon heads (out of use since the late 1800s) in the flesh of specimens. If this high longevity is correct, the bowhead whale may be the longest living mammal.

A smooth back with no dorsal fin, a blowhole placed in a high crown at the top of the head, and a thick layer of blubber for insulation equip them for this icy environment.

Bowheads skim-feed tiny crustaceans. A whale draws a huge amount of water into its mouth, then raises its tongue, which forces the water back out through baleen filters. The tongue then sweeps the trapped food back toward the throat. The diet consists of planktonic crustaceans, which are filtered through the baleen plates. Bowhead whales often skim-feed on the surface of the sea but also gather food from the sea floor.

Bowheads are social animals, and communicate through long-distance vocalizations, some carrying five to ten kilometres. Males become involved in showy bouts of breaching and fluke-slapping, probably because they are competing with one another for access to females. Bowheads are slow breeders, and sexual maturity may not be reached for 20 years. A single calf is born every three or four years after a gestation period of about 13 months.