Amidst environmental crises, soaring waste levels, and global dependence on fossil fuels, this book emerges as a significant contribution to redefining the path of sustainable development. Green Energy Circulation provides a comprehensive discussion on how Anaerobic Digestion (AD) technology can serve as a strategic solution for advancing the circular economy and transitioning towards a cleaner, more efficient energy system. Employing a scientific yet accessible approach, the author outlines the fundamental principles of the circular economy, the biochemical mechanisms of the anaerobic process, the potential of biogas and biofertilizer, and how AD technology can transform organic waste into high-value resources. Furthermore, the book presents global case studies from countries like Germany, Sweden, India, and Brazil, which have successfully implemented AD on a massive scale. The author emphasizes the critical importance of integrating the latest technologies such as the Internet of Things (IoT), artificial intelligence (AI), and circularity-based business models as keys to the successful implementation of AD, from household to industrial scales. Critical issues such as regulatory challenges, financing, public education, and cross-sector collaboration are also discussed in depth. This book is highly relevant for students, researchers, policymakers, environmental activists, and renewable energy practitioners. With a reflective yet data-driven presentation style, this book not only offers theoretical insights but also provides a practical roadmap for building a resilient and inclusive circular energy ecosystem for the future.