Cottontail rabbits are among the 16 lagomorph species in the genus Sylvilagus, found in the Americas.
In appearance, most cottontail rabbits closely resemble the wild European rabbit (Oryctolagus cuniculus). Most Sylvilagus species have stub tails with white undersides that show when they retreat; giving them their name, "cottontails". This feature is not present in some cottontails (for example, the underside of the brush rabbit's tail is gray), nor is it unique to the genus (for example, the European rabbit also has a white scut). The genus is widely distributed across North America, Central America, and northern and central South America, though most species are confined to particular regions.
For more information, visit the Wikipedia entry.