Preliminary experimental evidence shows that it is possible for an eavesdropping dolphin to discern object information from the returning echoes generated by the echolocation signals of conspecifics. Researchers have offered suggestions as to how this proposed ability may affect the behavior of wild dolphin species. A review of early and contemporary ideas, hypotheses and experiments concerning eavesdropping in dolphins is presented here, resulting in the development of a formalized, modern version of the ‘echoic eavesdropping’ hypothesis. The ecological implications of eavesdropping behavior remain unknown; refinement of the hypothesis and clarification of underlying assumptions are vital to our understanding of how echoic eavesdropping behavior might manifest itself in the social behavior of wild odontocetes. Suggestions for future research involving both echoic eavesdropping and a novel, alternative hypothesis (multi-source echoic eavesdropping) are offered. With the potential to elucidate many of the mysteries concerning dolphin biosonar use and dolphin behavior in general, echoic eavesdropping is an idea that deserves future attention.