(from the chapter) If outcomes from decades of public health and health behavior intervention research are to be translated into major health improvements, we must understand factors that support and inhibit the uptake of disease. However, knowledge and resources necessary to implement effective programs and interventions were lacking until recently. The Diffusion of Innovations model has been used widely to understand these processes and as a foundation for dissemination strategies. Key constructs and concepts are defined in this chapter, and some of the most important methodological and research issues that need to be addressed in the future are discussed. There now is an increasing emphasis on and need to disseminate complex, multi component, and multilevel programs to address health behavior issues such as tobacco control, HIV/AIDS control, and increased physical activity. A major challenge for the future is more frequent and better application of the Diffusion of Innovations model to complex innovations and to use evaluation designs that are rigorous, feasible, and relevant to real-world settings. Probably the most important practical lesson arising from diffusion research in recent years has been the importance ofof an innovation, the adopting individual or organization, and the environment or context where the process takes place.