Australian Mammals: Living and Extinct
- Species profiles including habitats, characteristics, behavior, breeding cycles, feeding, images and range maps.
- http://www.amonline.net.au/mammals/

Wildlife Africa: Animal Behavior: Mammals
- Notes on the habitat, habits, diet and breeding behavior of some of the larger African mammals.
- http://www.wildlifeafrica.co.za/animalbehavior.html

Natural History Collections: Mammals
- An introduction to the biology of the placental mammals, the monotremes and the marsupials.
- http://www.nhc.ed.ac.uk/index.php?page=24.134.165

Mammals of Kansas
- Checklist, descriptions, and photos.
- http://www.ku.edu/~mammals/

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.
- http://nhm.ku.edu/mammals/

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.
- http://www.press.jhu.edu/books/walkers_mammals_of_the_world/

Mark Kostich - Rare and Endangered Mammals
- High quality images of species from around the world. Includes Giant Muntjac, Owston's Civet, Binturong, Spotted Linsang, Pangolin, Yellow Throated Marten, Indian Civet, Genet Cat, Sun Bear, Pygmy Loris, and Slow Loris.
- http://www.kostich.com/other_mammals.htm

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.
- http://www.animalinfo.org/

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.
- http://www.nmnh.si.edu/vert/mammals/mammals.html

MAMMFAUN
- A bibliography of publications concerning the geographical distribution of mammals.
- http://www.wku.edu/~smithch/mamm/MAMMFAUN.htm

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).
- http://www.ucmp.berkeley.edu/mammal/mammal.html

Tasmanian Mammal List
- Guide to Tasmania's mammals.
- http://www.parks.tas.gov.au/wildlife/mammals/Tasmlist.html

Mammals of Texas
- Guide to the 181 species of Texas mammals, based on Davis and Schmidly's classic printed handbook.
- http://www.nsrl.ttu.edu/tmot1/

The Ultimate Ungulate Page
- Biology of the infraorder Ungulata and related groups, including Artiodactyla, aardvarks, elephants, hyraxes, sea cows, and Perissodactyla.
- http://www.ultimateungulate.com/

Class Mammalia
- Introduction to mammals, with detailed information about subclasses and orders of mammals, from the Animal Diversity Web.
- http://animaldiversity.ummz.umich.edu/chordata/mammalia.html

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.
- http://www.nmnh.si.edu/msw/