The taxonomy and distribution of halocyprid ostracods from the Arabian Sea Region is reported, based upon samples collected in the Northwestern Indian Ocean within the framework of the Netherlands Indian Ocean Program (NIOP: 1992-1993), the U.S. Joint Global Ocean Flux Study (U.S. JGOFS: 1994–1996), and the U.S. Global Ocean Ecosystem Dynamics program (U.S. GLOBEC: 1995). Forty-one species from the following genera belonging to the family Halocyprididae are described, illustrated, and representative photographs are presented: Archiconchoecia, Alacia, Conchoecetta, Conchoecia, Conchoecilla, Conchoecissa, Discoconchoecia, Loricoecia, Mikroconchoecia, Orthoconchoecia, Paraconchoecia, Paramollicia, Platyconchoecia, Porroecia, Proceroecia, Pseudoconchoecia, Clausoecia, Kyrtoecia, Nasoecia and Euconchoecia. For fourteen species, members of the genera Macroconchoecia, Mollicia, Paraconchoecia, Metaconchoecia, Mülleroecia, Fellia, Halocypria and Halocypris, only carapace outlines are presented. Keys to the subfamilies, tribes, genera and species, and patterns of horizontal and vertical distribution of each described species in the Arabian Sea Region are also given. The data on occurrence of halocyprid species at each of the stations during the investigation period and the depth ranges of halocyprid species found in the analyzed material but not described in the present book are listed in appendices.