This book provides a monographic treatment of seven diaptomid genera, viz. Heliodiaptomus Kiefer, 1932, Allodiaptomus Kiefer, 1936, Neodiaptimus Kiefer, 1932, Phyllodiaptomus Kiefer, 1936, Eodiaptomus Kiefer, 1932, Arctodiaptomus Kiefer, 1932, and Sinodiaptomus Kiefer, 1932. It does not claim to be a revisionary work, although the diagnosis of certain genera has been revised. The species, as allocated to the above genera by Kiefer or their original authors, have been treated as such. notwithstanding the fact that the present position of certain species of Heliodiaptomus, Allodiaptomus and Neodiaptomus is indeed questionable. Keys are prepared for the first time for both sexes of all the species of all the genera except Arctodiaptomus, for which Kiefer's (1971, 1978) keys have been enlarged to accommodate other species of the world. No phylogeny has been followed while arranging the species or genera.