With over 409 human cases of avian influenza and over 256 deaths worldwide resulting from infection with avian influenza (H5N1), an influenza pandemic is still a real threat, especially with H5N1 continuing to evolve into antigenically distinct clades. The Food and Drug Administration (FDA) along with other national regulatory authorities (NRAs) recognize the important role that safe and effective vaccines will play in protecting the public health from the threat of an influenza pandemic. The challenges to the FDA and other NRAs are significant as regulatory agencies pursue the development of new scientific and regulatory criteria to evaluate vaccines against pandemic influenza strains for licensure. To this end, the FDA is actively utilizing current regulatory processes such as accelerated approval and priority review as well as developing the regulatory pathways needed to speed the availability of vaccines against pandemic influenza. In May of 2007, the FDA issued two final guidance documents, one describing the clinical data recommended to support the licensure of annual influenza vaccines, and the other describing the clinical data recommended to support the licensure of pandemic influenza vaccines. These guidances contain specific approaches outlined by the FDA to assist manufacturers in developing new vaccines to increase the supply of safe and effective influenza vaccines for both annual and pandemic use. In this article we define the nomenclature "pandemic" and "prepandemic," describe the regulatory pathway for licensing new influenza vaccines for pandemic and prepandemic use, and outline considerations for evaluating pandemic/prepandemic vaccines that have been formulated using new approaches such as cell culture and non-aluminum salt adjuvants.