'Linnaean classification is pre-Darwinian, yet evolutionary biologists continue to use it to describe life's diversity. In this clearly written and incisive book, Ereshefsky shows that this makes no sense. His message isn't just that the Linnaean system should be junked; in addition, Ereshefsky constructs a better system to take its place. This book is of practical importance to biologists, but its analysis of the relationship between theories and classification schemes will also be of compelling interest to philosophers of science.' Elliott Sober, University of Wisconsin, Madison