This textbook accommodates the two divergent developmental paths which have become solidly established in the field of fusion energy: the process of sequential tokamak development toward a prototype and the need for a more fundamental and integrative research approach before costly design choices are made. Emphasis is placed on the development of physically coherent and mathematically clear characterizations of the scientific and technological foundations of fusion energy which are specifically suitable for a first course on the subject. Of interest, therefore, are selected aspects of nuclear.