The replacement of fossil-derived compounds by bio-based fuels and chemicals is crucial for the implementation of a sustainable bioeconomy. In this context, microorganisms are key players for biofuels' production from renewable sources. Biotechnological biofuel production processes require conversion microorganisms capable of both efficiently assimilating renewable low-cost carbon sources and diverting their metabolisms towards the specific biofuel. Exploring the wide diversity of microorganisms available on Earth will surely aid to make the production of green fuels a reality. This book gives a wide overview of different microbial-based processes for green fuels production. The book also includes techno-economic analysis and highlights strategic, commercial and environmental interests in promoting green fuels. All these facts make this book very valuable not only for the scientific community but also for biofuel companies and policy makers.