There are two recognized subspecies of bald eagle with the larger subspecies, H. l. alascanus, being larger than the southern, nominate subspecies, H. l. leucocephalus.
The bald eagle is placed in the genus Haliaeetus (sea eagles).
The bald eagle was one of the many species originally described by Linnaeus in his 18th century work Systema Naturae, under the name Falco leucocephalus.
There are two recognized subspecies of bald eagle. Haliaeetus leucocephalus leucocephalus (Linnaeus, 1766) is the nominate subspecies. It is found in the southern United States and Baja California Peninsula. Haliaeetus leucocephalus washingtoniensis (Audubon, 1827), synonym H. l. alascanus (Townsend, 1897), the northern subspecies, is larger than the southern nominate leucocephalus. It is found in the northern United States, Canada and Alaska.
The bald eagle forms a species pair with the white-tailed sea-eagle (Haliaeetus albicilla) of Eurasia. This species pair consists of a white-headed and a tan-headed species of roughly equal size, though the white-tailed sea-eagle overall has somewhat paler brown body plumage. The two species fill the same ecological niche in their respective ranges. The pair diverged from other sea-eagles at the beginning of the Early Miocene (c. 10 Ma BP) at the latest, but possibly as early as the Early/Middle Oligocene, 28 Ma BP, if the most ancient fossil record is correctly assigned to this genus.