Diffusion studies of the “adoption of innovation” can potentially provide a basis for a quantitative, empirically-based theory of social change. However, before significant advances can be made in this direction, rigorous attention must be directed toward clarifying the meaning of the principal concepts of diffusion studies and toward increasing consistency in the use of standardized terms from one writer to another. Also, theoretical concepts from diffusion research need to be linked to more general sociological theory, insofar as this is available. The present paper suggests possible ways in which these tasks can be undertaken. It makes use of mass communication data on the diffusion of the major media through the American society to illustrate the advantages of the conceptual framework which it proposes.