Bitterns are a classification of birds in the heron family, Ardeidae, a family of wading birds. Species named bitterns tend to be the shorter-necked, often more secretive members of this family. They were called hæferblæte in Old English; the word "bittern" came to English from Old French butor, itself from Gallo-roman butitaurus, a portmanteau of Latin būtiō and taurus. Bitterns form a monophyletic subfamily in the heron family, the Botaurinae.

Bitterns usually frequent reedbeds and similar marshy areas, and feed on amphibians, reptiles, insects, and fish.

Unlike the similar storks, ibises and spoonbills, herons and bitterns fly with their necks retracted, not outstretched.