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 w 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 techlogies, CO2 abatement techlogies, and some potential tools (exergy, constructal theory, etc.) for design, analysis and performance improvement.