In 1999, the World Health Organization's (WHO) Department of Vaccines and Biologicals launched the Immunization Safety Priority Project with the aim of establishing a comprehensive system to ensure the safety of all immunizations given in national immunization programs. Countries are the primary focus of the project. WHO has a role, not only because of its technical and normative role, but also because of its privileged relationship with country authorities and other partners, and its global vision and mandate. The four major areas of focus in the project are to (1) promote and coordinate research and development of safer and simpler delivery systems; (2) ensure vaccine safety, from vaccine development all the way through clinical trials and vaccine distribution until use; (3) broaden access to safer and more efficient systems for vaccine delivery and management of sharps waste; and (4) establish efficient mechanisms to detect serious or potentially serious adverse events following immunization, and enable prompt and effective response. The project emphasizes the importance of advocating safety and building capacity at national levels.