Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouche and Charles Picard became the first to develop an oxygen-acetylene welding set-up in 1903. Pure oxygen, instead of air (20% oxygen/80% nitrogen), is used to increase the flame temperature to allow localized melting of the workpiece material (e.g. steel) in a room environment. A common propane/air flame burns at about 2,000°C, a propane/oxygen flame burns at about 2,500°C, and an acetylene/oxygen flame burns at about 3,500°C. Since iron melts at about 1,500°C (high carbon steel at about 1,150°C), air flames can achieve melting only in a specialized insulated furnace. Small, high-flow, oxygen flames provide enough heat flow to locally exceed the melting point in a large workpiece (e.g. sheet).

Oxy-fuel is one of the oldest welding processes, though in recent years it has become less popular in industrial applications. However, it is still widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-based artwork.