The concept of sustainable development was first introduced by the Brundtland Commission almost 20 years ago and has received increased attention during the past decade. It is now an essential part of any energy activities. This is a research-based textbook which can be used by senior undergraduate students, graduate students, engineers, practitioners, scientists, researchers in the area of sustainable energy systems and aimed to address some key pillars: better efficiency, better cost effectiveness, better use of energy resources, better environment, better energy security, and better sustainable development. It also includes some cutting-edge topics, such hydrogen and fuel cells, renewable, clean combustion technologies, CO2 abatement technologies, and some potential tools (exergy, constructal theory, etc.) for design, analysis and performance improvement.