Occupancy schedules and density affect building energy use and indoor air quality. ASHRAE promotes studying occupant behavior in buildings. Past research shows building systems don't always use energy efficiently or provide good air quality due to inaccurate assumptions about occupants. Providing accurate ventilation based on occupancy can save energy. However, current ventilation standards may not be enough to prevent virus spread. Using high-temperature cooling and increased air movement can improve ventilation without using more energy. Existing methods for monitoring occupancy and controlling building systems have strengths and weaknesses. Future research should focus on improving occupancy-based strategies.