The purpose of this study is to examine the theory of workmen's compensation, tracing its historical development and showing how the law evolved in the United States. Pertinent statutes and administrative and judicial decisions will be given to the evolution of the theory of compensable occupational diseases. Following an analysis of the occupational disease concept and the significance of this concept in modifying the basic theory, an effort will be made to evaluate the effect of this concept upon the meaning of the laws.