The marsupials are an important order of mammals that have evolved along lines parallel to eutherians. This book brings together what is known about one very important sense needed for survival - hearing. It documents various studies of the hearing capacities of marsupials and relates this information to their vocal behavior. To what sounds do marsupials respond? What are the spectra of their vocalizations? The organization of the brain auditory pathways of marsupials is compared with those of eutherian mammals and related to the structure of the auditory periphery. The fact that much of the early development of marsupial young occurs outside the mother's body enables the possibility of discoveries about the early development of brain and hearing relevant to all mammals.