Book excerpt: This book constitutes the refereed post-conference proceedings of the 8th EAI International Conference on Green Energy and Networking, GreeNets 2021, held in Dalian, China, June 6-7, 2021. The 31 revised full papers were carefully selected form 85 submissions. The papers are organized thematically in green energy, green communication and networking, intelligent lighting control, machine learning, nonlinear system and circuits, and image encryption. The papers present a wide range of applications in civilian and commercial areas to reduce the impact of the climate change, while maintaining social prosperity.