Resource constraints in both the public and the private sector limit investment in vaccine research and development. The choice of options is complicated by large variations in the severity and duration of disease-related conditions, the existing knowledge base for new vaccine development, the time and resources required to bring the vaccine to licensure and the expected utilization. This report presents a comprehensive model designed to help government decision makers set priorities for vaccine development. It can be used to assess new vaccine candidates or to reassess current contenders as additional information becomes available.