This book is designed with the objective of studying microalgae and its application in the widest sense. Microalgae offer various inherent advantages as they are capable of accumulating lipids (20-70%), and able to aid with the production of pigments, carbohydrates, and proteins. The book comprehensively covers microalgae isolation techniques, their cultivation, and wastewater treatment by microalgae as well as the impact on biomass, lipid extraction, biofuel, and utilization of residual biomass focusing on biorefinery approach. The volume discusses the conversion of defatted oiled microalgae biomass for different applications. Acknowledging these challenges, this book discusses the limitations, outcomes, and economic aspects