This book offers a comprehensive exploration of the history and development of power reactors worldwide, from their inception to the present day. It provides an in-depth analysis of light water reactors and their global technology, while also delving into the evolution of gas-cooled, heavy water, liquid metal-cooled, aerospace, and nuclear fusion reactors. By examining past advancements, this book equips readers with the insights necessary to apply lessons learned to future reactor development and utilization.