The book is designed to understand process of photosynthesis, the process that convert physical or radiant energy to chemical energy. The book summarizes about photosynthetic pigments, structures, mechanism, electron transport system, photo-phosphorylation, significance, Calvin Benson cycle and its regulation, C4 plants and its regulation, Crassuliaean Acid Metabolism (CAM), characteristics of CAM plants, mechanism and ecological significance in very simple way.