A detailed study of Neogene Ostracoda fauna has been made from closely sampled sections in the Adana and Antakya basins of southern Turkey. The Quaternary (Early Pleistocene) fauna studied has been obtained from the bore-holes drilled in the Mediterranean and in Cyprus. Some samples collected by Prof, P.C. Sylvester-Bradley from the Miocene and Pliocene of Cyprus have also been studied and compared. A Biozonation is proposed by means of Ostracod assemblages for the stratigraphic position of the sections studied. The Ostracoda assemblages are compared with those of Neogene stratotypes. It shows that most of the biozones can be recognized outside the studied area, particularly in Italy and in Greece. Paleoecological interpretations are based on the presence and relative abundance of indicator genera which may give a general idea about the depth and salinity of depositional environment. Four different types of realms are reflected in the Ostracoda assemblages (a deep open marine, a moderate marine, a shallow marine and a brackish environment) (Chapter I). The assumptions are made for the interpretation of paleo-environment and comparisons between the two basins (Chapter II). The systematic part of the research deals with about 200 species. A new genus Sylvestra and 73 new species are proposed. Two subgenera and some species are renamed (Chapter III).