The circular bioeconomy can be visualized as a set of ‘many through many to many’ relationships, connecting different types of biomaterials from a variety of source-sectors via diverse processes and technologies in biorefineries, to end-use applications availing of the resulting valorized bio-products. One end-use sector is the energy sector; the end-use applications being as sources of heat and electricity, and as transport fuels. The focus of the chapters in this book is on bioenergy and biofuels in a circular bioeconomy, while this introductory chapter is an overview of published research in this niche area