This open access book presents a vision of a future, where avatars play an integral role in shaping the fabric of our interconnected society. The book introduces the authors' ongoing efforts to advance avatar technologies and is structured into nine chapters. Chapter 1 discusses the potentially revolutionary impact of cybernetic avatars (CAs) as a new medium of communication, liberating individuals from physical barriers and creating more flexible work environments. Chapters 2, 3, and 4 present developments in CAs with advanced autonomous functionality. Chapters 5 and 6 discuss the creation of a CA platform that connects multiple operators and CAs. Chapter 7 explores the physiological and neuroscientific effects of avatars and other media on operators and users. Finally, Chapters 8 and 9 discuss the societal implementation of CAs. This book is stemmed from one of the Moonshot R&D projects funded by the Japan Science and Technology Agency (JST).