This is an archived recording of the 2021 online version of the course. The course materials and continuing education credits and/or professional development hours are not available. A comprehensive introduction to how ultraviolet germicidal irradiation (UVGI) can be used in conjunction with HVAC systems to improve indoor environmental quality (IEQ) and reduce airborne disease transmission is the focus of the course. The course surveys the history and development of UVGI from its beginnings in the 19th century to the present, describes the fundamentals of the germicidal action of UVGI and characteristics of UVGI sources, common system types and their applications, the economics of UVGI, and practical considerations including material degradation, maintenance and safety. Case studies are used to illustrate typical applications.