Plasma arc welding (PAW) can be defined as a gas-shielded arc welding process where the coalescence of metals is achieved via the heat transferred by an arc that is created between a tungsten electrode and a workpiece. This article discusses the melt-in mode and the keyhole mode of the PAW process, as well as the advantages and disadvantages. It describes the components of a basic PAW system, namely the power source, plasma control console, water cooler, welding torch, and gas supply system for the plasma and shielding gases. The article provides information on the applications of the PAW process and discusses the typical components and joints used. It concludes with information on personnel requirements and safety issues.