The genera Helice and Chasmagnathus include dominant species of eastern Asian salt marshes and estuarine environments. After the introduction of both taxa by W. de Haan in the Crustacean volume of the famous _Fauna Japonicap_ edited by Phillip Franz von Siebold, a tradition of lumping similarly looking crabs from South America, Australia, and New Zealand into these two genera has emerged. On the basis of partly novel character sets the present revision splits these artificial assemblages into mostly new homogeneous genera. It includes all known species of this complex in a single monograph with keys, diagnostic descriptions and detailed illustrations in order to allow proper identification and to make the historic record about the species available. This comprehensive volume will be of interest for taxonomists, ecologists and people interested in coastal the regional environments.