This monograph evolved from years of research into the auditory pathway and hearing of many species of marsupials. Its function is to give biologists, in par­ ticular neurobiologists, a broad description and review of what is known of the auditory sensory capacities and processing mechanisms in this large order of mammals. My initial interest in marsupials developed from collaborative work with Dr. Richard Gates at Monash and Melbourne Universities in the 1970s and by curiosity as to whether concepts about the auditory system was stimulated stemming from experiments mainly on domestic cats could be extended to mam­ mals of other orders. My subsequent interest in Australian marsupials, aroused by collaboration with Dr. John Nelson at Monash University in the 1980s and 1990s, concerned their auditory systems and behavior per se and not as primitive cousins of eutherians. More recently, I have collaborated with Dr. Bruce Masterton at Florida State University in studies of New World marsupials. His sad death in 1996 has robbed neurobiologists of one of our most provocative thinkers and hypothesis testers. I would like to thank the Department of Physiology at Monash University for making many facilities available to me, the National Health and Medical Research of Australia and the Australian Research Council for providing funds for Council research, and Jill Poynton and Michelle Mulholland, who illustrated this volume.