Mammal Species of the World - Names and literature citations for the 4,629 currently recognized species of mammals, in a taxonomic hierarchy that includes Order, Family, Subfamily, and Genus.

Class Mammalia - Introduction to mammals, with detailed information about subclasses and orders of mammals, from the Animal Diversity Web.

The Ultimate Ungulate Page - Biology of the infraorder Ungulata and related groups, including Artiodactyla, aardvarks, elephants, hyraxes, sea cows, and Perissodactyla.

Mammals of Texas - Guide to the 181 species of Texas mammals, based on Davis and Schmidly's classic printed handbook.

Tasmanian Mammal List - Guide to Tasmania's mammals.

UCMP Hall of Mammals - University of California Museum of Paleontology site providing an introduction the Class Mammalia and to the subcategories of mammals, including the marsupials, monotremes, multituberculata, and the eutheria (placentals).

MAMMFAUN - A bibliography of publications concerning the geographical distribution of mammals.

National Museum of Natural History Division of Mammals - With roughly 570,000 voucher specimens, by far the world's largest mammal collection. Located in Washington, DC, USA.

University of Kansas Natural History Museum Division of Mammals - The mammal collection is one of the largest in North America and the second largest university collection, with over 158,000 cataloged specimens.

Walker's Mammals of the World - Online version of the reference work by Ronald W. Nowak. Some sections are free, but subscription is required for most areas.

Terrestrial Mammals of the Arctic - Checklist of the 48 species.

Animal Info - Rare, Threatened and Endangered Mammals - Biology, ecology, habitat, and status of rare, threatened and endangered species of mammals and information on their native countries: biodiversity, ecosystems, population, and land use.