Some would say that electricity and hydrogen are the future sources of energy. This chapter emphasizes that over the past several decades, electricity has played a more and more dominant role in total energy consumption. There are many reasons for the chronological growth of electricity. Transportation industry is moving away from the internal combustion engine and moving toward electric vehicles. Home heating and cooling is relying more on heat pump, and solar energy. Portable electronic devices and all modern technological developments require electricity. The access of electricity is generally considered as necessity for the economic development and the improvement of quality of life, particularly for the developing country. The use of electricity has three components: generation, storage and transport. It is the generation part that has caused environmental issues due to the use of fossil fuels and emission of GHG. In recent years, the use of fossil fuels is being replaced by renewable fuels and nuclear energy when possible. The electricity can be generated by thermal, non-thermal and hybrid sources. This book is focused on advanced power generation methods using thermal sources. There are five thermal sources: combustion, nuclear heat, geothermal, solar and waste heat. The book also examines recent advances in the use of these sources. Chapter 1 outlines the organization of the book toward this objective.