We compare and contrast the signalling systems and social behaviors of Alligator mississippiensis, Crocodylus aculus, and Crocodylus mloticus. Our qualitative analysis focuses primarily on the behaviors of adults during three phases of reproduction: I. Defense of Territory and Courtship, II. Nesting and Incubation, and III. Hatching and Post Hatching. Signals and signal elements are very similar among the three species. For example, all have vocal, non-vocal acoustic, and visual signals, some transmitted through air or water and others through both media. In addition, each species' repertoire is composed of discrete, graded and complex signals. A few signals are unique to each species. However, their signalling systems differ in the temporal organization of the behaviors, and in the relative frequency in which certain functional groups of signals occuror in which signals occur in a particular sensory mode. Apparently, the signalling systems of C. acutus and C. niloticus are more similar to each other than either is to the signalling system of A. mississippiensis. The signalling systems of the crocodile species appear to be adapted to open water habitats in which visual signals are advantageous and to high density breeding groups and post-copulatory intersexual contact. In contrast, the Alligatorsignalling system appears adapted to a marsh habitat in which vocal signals are likely favored and to low density breeding groups.