Male fiddler and ghost crabs are unique among the Crustacea in their use of acoustical signals to call females during the breeding season. This paper reviews what has been learned about the sound-producing mechanisms, signal characteristics, calling range, detection abilities and the behavioural responses of the crabs to the calls. Evidence is also presented to suggest that species differences in call structure are heritable. Recent studies indicate that differences in calling behaviour in the two groups can be related to burrow zonation and access to water, and are best conceived as representing a continuum of change rather than two (or more) distinct patterns. Finally, directions of future research are outlined which emphasise where needed experimental studies would be most appropriate.