Marine phytoplankton, which regulates the oceanic food chain by controlling the first trophic level, was studied along the coastal waters of South Eastern Arabian Sea. The description and photographs included in this monograph is based on specimen collected from off Kochi waters, South Eastern Arabian Sea during the period 2010 to 2013. The book covers general introduction, materials and methods of collecting and preparing phytoplankton samples for identification, how to enumerate their abundance, identification keys and temporal variability of each phytoplankton. The identification key is provided with colour photographs which make the visual identification better. The photographs taken under LeicaTM Generic microscope by the authors are provided for visual reference. Each photograph is provided with description on how to identify the phytoplankton and their taxonomic position. The monthly variability of phytoplankton in the coastal waters of Arabian Sea was also provided for a period of 3 years. This monograph is the first comprehensive reference of its kind for the South Eastern Arabian Sea. The temporal variation of phytoplankton along coastal waters off Kochi will provide an insight to the species contributing the chlorophyll concentration in the region. This monograph will be beneficial for the higher secondary science students, College students (Botany and Zoology), research scholars, teachers and scientists working in the area.