DESC: Fusion research started over half a century ago. Although the task remains unfinished, the end of the road could be in sight if society makes the right decisions. This book is a careful, scholarly account of the course of fusion energy research over the past fifty years. Here the authors outline the different paths followed by fusion research from initial ignorance to present understanding, be it the understanding why a particular scheme would not work, or why it was more profitable to concentrate on the mainstream tokamak development. The book features descriptive sections in-depth explanations of certain physical and technical issues, scientific terms, and an extensive glossarythat explains relevant abbreviations and acronyms.