In 1974, Richard Lewontin published The Genetic Basis of Evolutionary Change, focusing enormous research attention on protein variation as both a model of underlying genetic variation and as a level of selection itself. Two decades later, scientific research has been shifted by the tremendous power of molecular biological techniques to explore the nature of variation directly at the level of DNA and the gene. The "protein chapter" is now drawing to a close. In this book, Mitton explains the questions that geneticists hoped to answer by studying protein variation, reveiws the extensive literature on protein variation, describes the successes and failures of the research program, and evaluates the results of a rich and controversial body of research. Yet Mitton's book is not merely a history of this research. It is a useful analysis for all scientists interested in the genetic structure and evolution of populations.