The California quail, also known as the California valley quail or Valley quail, is a small ground-dwelling bird in the New World quail family. These birds have a curving crest or plume, made of six feathers, that droops forward: black in males and brown in females; the flanks are brown with white streaks. Males have a dark brown cap and a black face with a brown back, a grey-blue chest and a light brown belly. Females and immature birds are mainly grey-brown with a light-colored belly. Their closest relative is Gambel's quail, which has a more southerly distribution and a longer crest at 2.5 in (6.4 cm), a brighter head and lacks the scaly appearance of the California quail. The two species separated about 1–2 million years ago, during the Late Pliocene or Early Pleistocene. It was selected as the state bird of California in 1931.

The New World quail are small birds, that despite their similar appearance and habits to the Old World quail, belong to a different family known as the Odontophoridae. In contrast, the Old World quail are in the Phasianidae family. The geographical range of the New World quail extends from Canada to southern Brazil, and two species, the California quail and the bobwhite quail, have been successfully introduced to New Zealand. The stone partridge and Nahan's partridge, both found in Africa, seem to belong to the family. Species are found across a variety of habitats from tropical rainforest to deserts, although few species are capable of surviving at very low temperatures. There are 34 species divided into 10 genera.