The tits, chickadees, and titmice constitute Paridae, a large family of small passerine birds which occur in the northern hemisphere and Africa. Most were formerly classified in the genus Parus.

These birds are called either "chickadees" (onomatopoeic, derived from their distinctive "chick-a dee dee dee" alarm call) or "titmice" in North America, and just "tits" in the rest of the English-speaking world. The name titmouse is recorded from the 14th century, composed of the Old English name for the bird, mase (Proto-Germanic *maison, German Meise) and tit, denoting something small. The spelling was influenced by mouse in the 16th century. Emigrants to New Zealand presumably identified some of the superficially similar birds of the genus Petroica of the family Petroicidae, the Australian robins, as members of the tit family, giving them the title Tomtit although, in fact, they are not related.

These birds are mainly small stocky woodland species with short stout bills. Some have crests. They range in length from 10 to 22 centimetres. They are adaptable birds, with a mixed diet including seeds and insects. Many species will live around human habitation and come readily to bird feeders for nuts or seed, and learn to take other foods. In Britain, Great Tits and Blue Tits learned to break open the foil caps sealing bottles of milk that had been delivered to homes to get at the cream floating on top.