Dr. Blandau presents an outstanding text in reproductive biology, dealing with the mammalian blastocyst. At the 1969 Lake Wilderness conference, he and other notable scientists worked toward a better understanding of the complex embryo-uterine interrelationships as well as a new prospective on contraception. They strove to give the physician basic fundamental concepts to control the expanding world population. High quality photographs, diagrams, and tables, combined with some 1,300 references on over 500 subjects, portray present-day blastocyst biology. One ponders over the many conflicting results and the inventory of unanswered questions which stagger our imagination. However, it seems quite likely that much of the data obtained from animals can be extrapolated and applied to man. Morphologic, biochemical, and developmental similarities exist among the pre-implantation stages of mammals. The blastocyst contains paternal elements foreign to the mother so that implantation may be considered a graft of alien tissue. Yet rejection marks the