Contains entries that provide information on the physical characteristics, geographic range, habitat, diet, behavior, reproduction, and conservation status of 141 families, and 265 species of mammals, and includes range maps, photographs and illustrations, and resources for further research.

Vol. 1. Echidnas to armadillos -- v. 2. Hedgehots to bats -- v. 3. Primates to true seals -- v. 4. Dolphins to antelopes -- v. 5. Pangolins to sengis.