This book describes the journey to produce viable fusion energy. This journey has not been smooth, and significant challenges remain, yet the existential need to produce non-carbon-producing forms of energy is so profound that governments and firms around the world are rapidly increasing their investments in this new kind of energy production.  Fusion energy holds the possibility of providing unlimited, sustainable power, and this book tells the story of its history and development, and its current progress as it moves from research to commercial production. It is a story of the importance of basic research and the challenges of turning it into commercial use. Fusion energy has progressed from the thinking of great scientists, such as Curie and Einstein, to the problems faced by engineers of designing and building machines that operate at temperatures ten times hotter than the centre of the Sun.   Fusion energy is a story of humanity at its best, of scientists, engineers, policymakers, and businesspeople working together and driven to solve a problem that threatens humankind?s existence as we know it.