Gene therapy is now being studied for the treatment of a wide variety of acquired and inherited diseases. Viruses used as vectors for gene transfer include retroviruses, adenoviruses, vaccinia viruses, adeno-associated viruses, and herpesviruses. These vectors, developed in the laboratory and in animal studies, are now being introduced into the clinical arena. Infection control practitioners will be involved invariably in reviewing the use of these agents in their clinics and hospitals. This review summarizes key aspects of the more common vectors and makes recommendations for infection control.