This paper summarizes key behavioral research contributions to the promotion of healthful diets and identifies the outstanding behavioral research needs that could lead to positive dietary changes in the United States. Nutrition plays an important role in the initiation, promotion, and progression of cancer. Dietary guidelines for health promotion and cancer prevention recommend diets that are lower in fat and higher in fiber, fruits, and vegetables. Behavioral research on dietary change has become more rigorous and sophisticated in the past decade, with noteworthy contributions in four areas: behavioral research within clinical trials, self-help or minimal contact intervention strategies, school nutrition programs and services, and advances in the development of measures. Work in progress includes large-scale randomized intervention trials, with the majority of funding for studies to increase fruit and vegetable consumption. There are many needs for further research. Six priority areas for behavioral research are identified and discussed: (1) determinants of dietary behavior and change processes; (2) policy, environmental, and organizational interventions; (3) studies of dietary change and exercise and interventions with persons at high risk for diet-related cancers; (4) methodological research; (5) research on diffusion and dissemination; and (6) systematic behavioral research on dietary change in clinical trials. A concerted research effort in the area of dietary change has great potential benefits for cancer prevention and control and for public health in general.