Marine nematodes are one of the most widespread and abundant group of animals belonging to the Phylum Nematoda. They play a significant role in marine environment and are widely used as pollution indicator in biological monitoring. Pakistan has 1000km long coastline stretching from Sir Creek on the Southeast to Jiwani on the West near Iranian border. The coastal and inshore inhabitants of Northern Arabian Sea were investigated. The aim of this book is to gather the information of marine nematode fauna including the descriptions of all new and known nematode species reported from Pakistan. Diagnostic characters of the order, suborder, super-family, family and genera have also been incorporated along with illustrations and photomicrographs. Taxonomically the nematode fauna of Arabian Sea consisted of 147 species and 107 genera belonging to eight orders. It is hoped that this information will provide a valuable source and would prove useful and informative for students and younger scientists who are working in marine Nematology.