Playback is the technique of rebroadcasting natural or synthetic signals to animals and observing their response. The ability to present a putative signal in isolation, without the potential confounding effects of other activities of the signaller, is the main reason for the depth and range of our knowledge of communication systems. To date, playback of sound signals has predominated, but playback of electric signals and even video playback of visual signals suggests that playback will become just as prevalent in studies of communication in other sensory modalities. This book is one of the outcomes of a workshop on playback held at Thombridge Hall in the Peak District National Park, England during August 1991. There were two reasons for organising the workshop. First, the considerable and lively debate in the literature about the design and analysis of playback experiments -the pseudoreplication debate -was in danger of generating more heat than light. A workshop forum seemed the obvious place to clarify and, if possible, resolve the debate. Second, with the number of new playback and analysis techniques increasing rapidly, it seemed an opportune moment to discuss these techniques and to review some rapidly developing areas of interest in sound communication.