This chapter contains sections titled: Introduction The Players: Phytoplankton Community Composition and Function Spatial and Temporal Patterns of Phytoplankton Biomass and Productivity Factors Controlling Phytoplankton Productivity and Community Composition Human and Climatic Impacts on Coastal Phytoplankton Dynamics Harmful Algal Blooms Nutrient Management of Phytoplankton Production and Composition Acknowledgments References