The function of refrigerant as a fluid used for heat transfer has not changed since the development of the first refrigerating system. Today, as in that first system, the refrigerant absorbs heat and transfers it at a higher temperature and a higher pressure, usually with a phase change. However, as the heating, ventilating, and air-conditioning (HVAC) industry has evolved and expanded, refrigerants also have changed over the years, mainly in response to safety and environmental concerns. Now the industry is moving to a new set of refrigerants developed in the last five years to address climate change issues. This newsletter will describe the benefits and challenges presented by these new refrigerants and discuss the current state as well as changes in the standards and codes that guide the application of refrigerants in HVAC equipment.