The book begins by illustrating vividly the differences among mammals--by showing the skulls of many species, from rabbits to seals to aardvarks to shrews. There follows a brief discussion of the evolution of mammals and their diversification over time.

After that, subjects vary, from coats and fur to the use of tails to breeding to keeping clean and so on. The book closes with a fascinating discussion of "mammal detectives," people who use their knowledge of nature to better understand fellow mammals. "Clues" include teeth, bones, furs caught on fences, and so on.