This paper begins with a broad review of food security in the developing world. I argue that technological change has made a key contribution to improving food security wherever it has been achieved and that plant sciences can contribute in the future. Potential contributions by plant scientists will have to be funded through development assistance. A perspective on development assistance and the role of assistance to agricultural research in particular provides a useful background to the consideration of how to set priorities for research using information on what is needed and what can be done. Optimizing the contributions of research entails five steps: (1) determine the specific objective, (2) identify alternatives to address the objective, (3) choose a method by which to set priorities, (4) apply the selected method to quantify priorities, (5) allocate available funds among the priority alternatives. Finally, it is important to take a long-term view and continue supporting the research long enough to make a difference. The paper discusses these steps, illustrates how such an approach might be applied and demonstrates the importance of applying economic criteria to research resource allocation.