In a recent publication (Historical perspectives: Advances in studies of avian sound communication. Condor, 96, 817-830, 1994) Luis Baptista and Sandra Gaunt present a review of the development of avian bioacoustics during the last four decades since the first application of the sound spectrograph in this field. As is already evident from the chapter headings in their publication, scientific analysis of avian sound communication revolves around one pivotal theme: song. In the study of sound communication of mammals there is no such central issue. Even very detailed recent accounts of a mammalian species' behaviour often present no more than anecdotal data on its vocalization, whereas for birds there is a growing number of monographic treatises, handbooks and, most recently, CD-ROMS with detailed descriptions of the species' acoustic communication signals, often including sonagrams, representing an integral part of the information provided on a species. In trying to present a review of the development of mammalian bioacoustics over the past four decades it becomes clear early on that despite the same technical equipment for sound recording and analysis having been available as for bird studies, the current state of knowledge on sound communication in mammals is considerably less substantial and homogeneous than in birds, especially songbirds. Comprehensive technical studies of vocalization in a large number of species of a taxon, contingent analyses of e.g. ontogeny of vocalization, hearing, sound production, etc., which provide the basis for an understanding of the acoustic communication system of these species, are largely restricted to three mammalian orders: bats (Chiroptera), cetaceans (Cetacea), and primates (Primates). For the former two it is predominantly not their intraspecific acoustic communication which is studied best but their echolocation signals, so this is a specific situation. Analysis and understanding of sound communication in most other mammalian orders is fragmentary at best. It is argued that in most mammalian groups there is a large backlog demand for basic descriptive studies with a primarily structural classification of the sound repertoire as the essential prerequisite for any further analysis.