The circular bioeconomy can be visualized as a set of “many-through-many-to-many” relationships. It connects 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; 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 a very brief overview in this niche area. © 2025 Elsevier Ltd. All rights are reserved including those for text and data mining AI training and similar technologies.