Volume I of East African Mammals contains introductory chapters on method, the East African environment vegetation, the Bwamba Forest, time perspectives on mammalian evolution, and mammalian anatomy. The major portion of the book is devoted to the study of primates, species by species, until all that occur in East Africa have been illustrated and their behavior, ecology, and anatomy discussed.

In each volume Kingdon combines his text with hundreds of finished drawings and quick sketches, the latter a form of field note that provides an incomparable description of the animal's movements and personality. Kingdom explains his drawings "as a wordless questioning of form. . . . The probing pencil is like the dissecting scalpel, seeking to expose relevant structures that may not be immediately obvious and are certainly hidden from the shadowy world of the camera lens." As an artist, Kingdon's achievement has been compared with Audubon's; as a scientist, his work has made these volumes indispensable to any serious student of East African mammals.