Demands for better diffusion of social studies instructional materials became widespread in the 1960s and early 1970s. These demands were largely in response to teachers' curiosity about the vast quantities of new social studies materials; to curriculum developers' desire that their materials be adapted; and to the public insistence on the best results for every educational dollar. A wide variety of models responded to this need for diffusion. Among these models, four are particularly important. The first, the Research, Development, and Diffusion model (R, D & D) is based upon a system of role specialization in which developers design and test innovations while diffusion specialists demonstrate and disseminate the innovation. R, D & D diffusion projects are conducted by professionals, materials based, and often well financed. A second model, the Social Interaction model (S-I) emphasizes the informal social networks through which information flows--such as state social studies councils. A major advantage of this model is that it stresses face-to-face contact at the local level. A third model, the Problem Solver (P-S), focuses upon serving user needs. The client centered focus of the P-S model typically results in a high degree of local commitment to instructional change efforts. The fourth model, Linkage Process, emphasizes the process whereby users interact with resource systems. This model is characterized by a two-way flow of information and is, generally, the most adaptable to a wide range of situations. (Author/DB)