Bats are highly gregarious mammals that have been extensively studied for their ability to echolocate (i.e., gain information from the echoes of ultrasonic calls) to navigate and find food. Perhaps less well studied are social vocalizations, which bats use to communicate with conspecifics. Some bat species have been shown to possess rich vocal repertoires, supporting intricate social interactions. While the roost is likely where the majority of a bat's social interactions occur, on account of higher densities, there are also behavioral contexts that occur predominantly, if not solely in flight, that are associated with social calls. Bats exhibit an extensive range in social group size, social group organization, and mating systems, making them interesting for comparative, phylogenetically controlled analyses. Group size is often correlated with vocal complexity, as more complex vocalizations can encode more information about individual identity. Vocal learning has been observed in some species of bats. The full vocal repertoires of relatively few bat species have been studied thus far, as they are nocturnal, volant animals that produce predominately ultrasonic vocalizations. With more data available, bats would be a very useful taxon for studying the evolution of social communication, as they exhibit not only a high diversity of social group size and complexity but also sophisticated vocalizations. Social vocalizations can be structurally diverse and are highly important for bat sociality. Calls often vary notably between species. Research in this field has barely scratched the surface, and there is still much to learn about social communication in bats.