6G is currently under definition, often being addressed from a plain telecommunications perspective as an evolutionary paradigm that represents an extension of 5G. Having as its horizon 2030, 6G initiatives are being deployed across the globe, to further ignite the development of 6G services. In its philosophy core, 6G embodies the "human in the loop" principle. The research effort aimed at 6G requires an interdisciplinary approach that ignites discussion across different key technological sectors, ranging from communications to services and business cases. The contribution of this book to research in the field concerns an evolutionary and interdisciplinary design of 6G as a paradigm that can be addressed by working together the four different computational areas of CONASENSE: communications; satellites and navigation; sensing; services. This book starts with a perspective on 6G challenges towards sustainability and addressing new business models, moving on to key topics concerning communications. It ends with chapters focusing on 6G service design. This book is, therefore, envisioned to assist in developing critical thinking to back up novel networking, applications, and services towards 6G.