Renewable energy source in general, and algal biodiesel in particular has the potential to provide energy services with zero or almost zero emission. Large-scale introduction of biomass energy could contribute to sustainable development on environmentally, socially and economically. Among biomass, algae usually have a higher photosynthetic efficiency than other biomass. As part of the photosynthesis process, algae produces oil and can generate 15 times more oil per acre than other plants used for biofuels, such as corn and switchgrass. Algae can grow in salt water, freshwater or even contaminated water.  In fact algae are the highest yielding feedstock for biodiesel. It can produce up to 250 times the amount of oil per acre as soybeans. The main purpose of this book is to sharing knowledge and discussing in detail related to algal oil from macroalgae as a sustainable feedstock for production of biodiesel that could be used as a renewable liquid fuel in existing diesel engine