The transition of refrigerants is a critical process driven by environmental concerns, regulatory changes, and technological advances. For decades, chlorofluorocarbons (CFCs) and later hydrochlorofluorocarbons (HCFCs) were widely used in refrigeration and air conditioning because they were stable, efficient, and relatively safe to handle. However, scientific research demonstrated that CFCs and many HCFCs contribute significantly to depletion of the stratospheric ozone layer, which protects life on Earth from harmful ultraviolet radiation.In response, the international community adopted the Montreal Protocol, a landmark environmental agreement that mandated the phase‑out of ozone‑depleting substances. This agreement triggered an initial refrigerant transition from CFCs and HCFCs to hydrofluorocarbons (HFCs), which have no ozone depletion potential. HFCs quickly became the dominant refrigerants in many sectors, including residential and commercial air conditioning, refrigeration, and automotive cooling.Over time, another environmental issue emerged: although HFCs do not damage the ozone layer, many of them have very high global warming potential (GWP). This means that, kilogram for kilogram, they can trap far more heat in the atmosphere than carbon dioxide. As climate change became a pressing global concern, policymakers, researchers, and industry professionals recognized that a second major transition in refrigerants would be necessary.The Kigali Amendment to the Montreal Protocol was adopted to address this challenge. It sets a schedule for the gradual reduction in production and consumption of high‑GWP HFCs, encouraging the development and adoption of lower‑GWP alternatives. As a result, the industry is moving toward next‑generation refrigerants, including hydrofluoroolefins (HFOs), natural refrigerants such as carbon dioxide, ammonia, and hydrocarbons, and optimized blends designed to balance performance, safety, and environmental impact.This transition is complex because refrigerants must satisfy multiple requirements simultaneously. They need to provide good thermodynamic efficiency, operate safely under intended conditions, be compatible with system materials and lubricants, and comply with evolving regulations. Lower‑GWP refrigerants often introduce trade‑offs. For example, many natural refrigerants and some HFOs are mildly flammable or toxic, which requires updated safety standards, revised building codes, and new system designs. Carbon dioxide systems operate at much higher pressures, demanding specialized components and engineering approaches.Energy efficiency is another central concern. A refrigerant with low GWP but poor efficiency may increase indirect emissions from power generation, offsetting some of the climate benefits. Therefore, system optimization, improved heat exchangers, advanced controls, and careful charge management are integral to the refrigerant transition. Life‑cycle climate performance, which considers both direct emissions from leaks and indirect emissions from energy use, is increasingly used as a holistic metric.Training and education also play a vital role. Technicians, system designers, and building operators must learn new handling practices, safety procedures, and diagnostic methods. Policy frameworks, incentives, and standards help guide markets toward sustainable solutions while ensuring reliability and safety for end users.Ultimately, the refrigerant transition represents a broader shift toward climate‑conscious cooling. As global demand for air conditioning and refrigeration grows with urbanization and rising temperatures, adopting low‑GWP refrigerants and high‑efficiency systems is essential to limiting environmental impact while maintaining comfort, food safety, and industrial productivity.