This book covers all major aspects of green communications. It discusses theory and practical issues, introduces fundamental principles, and considers both green wired and wireless communications. In the information and communication technologies industry, which is becoming a major consumer of global energy triggered by the telecommunication network operators experiencing energy cost as a significant factor in profit calculations, researchers have started to investigate various approaches for power consumption reduction. Standards bodies are already developing standards for energy-efficient protocols. This book aims to increase understanding of relevant issues and further the development of strategies and techniques; it also discusses the ICT industry's role in helping other industries reduce energy consumption.