Previous work on the reproduction of marsupials is mentioned briefly and the taxonomy of Setonix brachyurus Quoy and Gaimard, the animal chosen for this investigation, is discussed. The feeding in captivity, surgery, methods of taking vaginal smears, and histological methods are described. Anatomically the reproductive system of Setonix is similar to that of other marsupials. There are two ovaries, two uteri, and two lateral vaginae. The vaginal culs-de-sac are connected to the urogenital sinus, forming a pseudo-vaginal canal which remains open after the birth of the first young. The reproductive system differs from that of the true kangaroos and resembles that of the rat kangaroos in possessing an anterior vaginal expansion. Some preliminary observations on breeding are recorded, with some details of growth rates, feeding, etc. of pouch young.