The use of veterinary biologicals is an integral component of poultry health programs. All veterinary biologicals are licensed and sold by manufacturing firms under strict regulation by the U.S. Department of Agriculture to ensure purity, potency, efficacy, and safety of the product. The licensing process for a new vaccine is a complex process involving a defined set of studies for each type of vaccine that are performed by the biologics firm, according to approved protocols, with results submitted to the Center for Veterinary Biologics for review. There are 10 classifications of veterinary biologicals and four types of licenses. Manufacturing and testing procedures are also defined within the licensing process. Licensing requirements were initially codified into law. In addition, guidance documents in the form of memoranda and notices have been published to address licensing for additional classes of vaccines and disease agents. This overview of vaccine licensure in the United States is offered to provide a better understanding of the process, the participants, and the factors that influence the time required to produce a commercial product.