A total of 15 communities of ostracods have been recorded based on the dominant species in the bottom sediments sampled at 204 stations in the Caspian Sea. The distribution of the communities is determined by the bathymetric zonality of the sea, the currents, the topography of the water mass boundaries, the hydrochemical parameters of the water, the continental runoff, and the concentrations of O and C in the water and sediments.