This review is an updating of the paper by Frazier et at. 13 in which 30 individual cells and 8 cell clusters were identified in the abdominal ganglion of of Aplysia californica on the basis of morphological, physiological and pharmacological criteria. Since that time, a number of neurobiological studies have utilized the neurons of the abdominal ganglion for behavioral studies. Based on these new investigations, 32 additional cells and 2 additional cell clusters have been identified, bringing the total of identified cells in the ganglion to 62 individual cells and 10 cell clusters. Additional features of the previously identified cells have also emerged. Much of the new information concerns the role of identified cells in behavior. We have summarized the current list of identified cells in the abdominal ganglion emphasizing these behavioral features. We also review the known synaptic connections made by identified interneurons in the ganglion. Included are descriptions of 6 new interneurons that connect to other cells in the ganglion. A major conclusion from this survey is that behavioral criteria permit resolution between cells in identified cell clusters that could previously not be distinguished using other criteria.