This book focuses on tritium as a fuel for fusion reactors and a next-generation energy source. Following an introduction of tritium as a hydrogen radioisotope, important issues involved in establishing safe and economical tritium fuel cycles including breeding for a fusion reactor are summarized, these include the handling of large amounts of tritium: confinement, leakage, contamination, permeation, regulation and tritium accountancy, and impacts on surrounding areas. Targeting and encouraging the students and technicians who will design and operate fusion reactors in the near future, this book offers a valuable resource on tritium science and technology.