There are more than 6000 species belonging to twenty-seven orders in the Class Mammalia. Comparative studies of this diverse and magnificent array of extant species provide valuable opportunities to formulate and test hypotheses concerning the evolution of reproduction. This is the first book to explore, in depth and breadth, the complex interrelationships that exist between patterns of mating behaviour and the evolution of mammalian reproductive anatomy and physiology. It focuses upon the role that copulatory and post-copulatory sexual selection have played during the evolution of the monotremes, marsupials and placental mammals, and examines the effects of sperm competition and cryptic female choice upon coevolution of the genitalia in the two sexes. In addition, due weight is also given to discussions of the modes of life of mammals, and to the roles played by natural selection and phylogeny in determining their reproductive traits.