At the present time it is estimated that the process of development of a vaccine from discovery to licensure takes approximately 18-20 years and costs in excess of US$500 million. For "routine" vaccines, the case for developing a vaccine is straightforward in terms of economics and large scale public health utilization each year. For vaccines used for biodefense and emerging diseases, the considerations are somewhat different as the vaccine may not be needed every year to control outbreaks and may be stockpiled only as a countermeasure that hopefully may never be needed. Furthermore, efficacy trials are often difficult as the natural disease may be rare or not present. Consequently, animal models will play a critical role in demonstrating efficacy. Nonetheless, the vaccine pathway still requires the same fundamental components of basic science/discovery, preclinical development, clinical trials, registration/licensure, and a plan for implementation.