IAVI is a global not-for-profit, public-private partnership whose mission is to ensure the development of a preventive HIV vaccine for use throughout the world. This brochure details what IAVI is doing to achieve its objectives, explains why a vaccine is needed and what sort of impact it might be expected to have on the AIDS pandemic. It also lays out the scientific challenges that have impeded the development of a sufficiently effective vaccine and what researchers are doing to overcome those obstacles.