The article introduces the basics of heating, ventilating, and air conditioning (HVAC) systems. It covers the history, uses, and main processes of HVAC, including the seven major air-conditioning processes and the five main aspects that affect occupant comfort. HVAC systems range from simple stoves to complex air-conditioning systems used in submarines and space shuttles. The chapter emphasizes the importance of considering various factors beyond just maintaining comfortable temperatures when designing HVAC systems. It provides fundamental concepts and terminology used by designers to make decisions about system design, operation, and maintenance.