This classic book on the history of developments in transuranium elements presents the story of the development of plutonium, chemical properties of the actinide elements, nuclear properties of the transuranium elements, and future synthetic elements. The first chapter emphasizes the contribution of the chemists and metallurgists in the laboratory who actually isolated plutonium and characterized its properties. It provides lucid descriptions of the chemical separation of plutonium from uranium and fission products in irradiated uranium. This separation was critical to the production of plutonium used in nuclear weapons. The book is based on a series of lectures Professor Seaborg gave at Yale University in May 1957.