The American Yellow Warbler (Setophaga petechia, formerly Dendroica petechia) is a New World warbler species. Sensu lato, they make up the most widespread species in the diverse Setophaga genus, breeding in almost the whole of North America and down to northern South America. Other than in male breeding plumage and body size, all subspecies are very similar. Winter, female and immature birds all have similarly greenish-yellow upper-sides and are a duller yellow below. Young males soon acquire breast and, where appropriate, head coloration. Females are somewhat duller, most notably on the head. In all, the remiges and rectrices are blackish olive with yellow edges, sometimes appearing as an indistinct wing-band on the former. The eyes and the short thin beak are dark, while the feet are lighter or darker olive-buff.
The 35 subspecies of D. petechia sensu lato can be divided into three main groups according to the males' head color in the breeding season. Each of these groups is sometimes considered a separate species, or the aestiva group (Yellow Warbler) is considered a species different from D. petechia (Mangrove Warbler, including Golden Warbler); the latter option is the one currently accepted by the International Ornithological Congress World Bird List.