Microphytoplankton community studies forms an integral part of the productivity pattern analysis of marine ecosystem. While considering Arabian sea, particularly northern counterpart (Northern Arabian sea) the productivity studies are gaining much attention in the recent years. The winter time convective mixing driven by density gradient of the water column and associated biological production magnetized a few biogeochemical studies in the region. However in depth studies or checklists on the major primary producers, microphytoplankton (20-200 µm) is still vague here. This book describes in detail on the community structure of microphytoplankton of north eastern Arabian sea during the productive winter monsoon period. Variations in microphytoplankton community in accordance with the physico-chemical factors as well as its responses during the transition from winter to spring inter monsoon were also analyzed. The book provides a first of its kind knowledge on the major primary producers of the region. With the baseline data obtained further trophodynamic studies can be initiated in the complex productive north eastern Arabian sea ecosystem that is still remaining unexplored.