This chapter addresses the role of infection prevention and control in the environment with a specific focus on heating, ventilation, and air conditioning systems in healthcare facilities. Maintaining both comfort and safety of indoor air quality in healthcare facilities is essential for all occupants. Specifically, poor design and installation, system performance problems, and inadequate maintenance of heating, ventilation, and air conditioning systems have all been associated with transmission of airborne infectious agents and/or building-associated illness. Environmental containment/mitigation of airborne infectious agents (e.g., Mycobacterium tuberculosis, Aspergillus spp., varicella zoster and measles viruses, plus newly emergent pathogens such as severe acute respiratory syndrome-associated coronavirus) and preparedness for deliberate use of pathogens as bioweapons are vital areas the infection preventionist can provide expertise for their affiliated facility.