Ten bonobos (Pan paniscus), housed in three separate subgroups at the San Diego Zoological Garden, were observed for 288 hours over a four-month period. The colony included one adult male, two adult females, two adolescent males, four juveniles, and one infant. Data on 5,135 sequences of social behavior were collected either as spoken accounts or as video recordings. In addition, high-quality sound recordings were obtained for spectrographic analysis. The data were subjected to a quantitative analysis of probabilities of association between 44 communicative behavior patterns and 40 different context types. The paper treats each communicative behavior pattern separately, providing a) its frequency, b) the most common inter-individual directions of performance, c) characteristic contexts, d) a description, e) a commentary on its possible functions, and 1) a comparison with the behavior of chimpanzees (Pan troglodytes). The study shows that, while the behavioral repertoires of the two Pan species are fundamentally similar, interesting differences exist in their vocal repertoires, sexual behavior, and agonistic behavior. The bonobo's voice has a higher pitch, and many of its vocalizations are structurally different from homologous chimpanzee vocalizations. The greatest difference concerns the long-distance hooting calls of the two species. The bonobo's sexual behavior is much more elaborate than the chimpanzee's, including ventro-ventral copulation, and "GG-rubbing" between adult females. Sexual forms of contact seem to serve many of the reassurance and reconciliation functions fulfilled by nongenital contact forms in the chimpanzee. Finally, the bonobo's agonistic behavior is less elaborate and appears more controlled than the chimpanzee's.