The outbreaks of myxomatosis among rabbits in Australia in 1950 and in Europe in 1952 provided scientists with opportunities of observing the course of the interaction of a very lethal virus disease with a large population of highly susceptible mammals, i.e. with a model system to study the evolution of an infectious disease, and the effects of an infectious disease on the evolution of a mammal. This scientific account of the spread of the disease in Australia and Europe, of its effects upon rabbit numbers, and of the genetic changes that occurred in parasite and host, is of great interest to ecologists, virologists, parasitologists, mammalian zoologists, geneticists, agriculturists, and public health workers, as well as to those directly concerned with rabbit raising or control.