Pygmy owls are members of the genus Glaucidium. They belong to the typical owl family, Strigidae, one of the two generally accepted living families of owls. The genus consists of about 26 to 35 species distributed worldwide. The exact number of species is somewhat disputed.
These are mostly small owls, and some of the species are called "owlets". Most pygmy owl species are nocturnal and hunt mainly large insects and other small prey.
The supposed prehistoric species "Glaucidium" dickinsoni is now recognized as a burrowing owl, probably a paleosubspecies providentiae. Bones of an indeterminate Glaucidium have been recovered from Late Pliocene deposits in Poland (Mlíkovský 2002).