Metal Inert Gas (MIG) welding or Metal Active Gas (MAG) welding, also known as Gas Metal Arc Welding (GMAW) is a semi-automatic or automatic arc welding process in which a continuos and consumable wire electrode and a shielding gas are fed through a welding gun. A constant voltage, DC power source is most commonly used with MIG/MAG, but constant current systems, as well as AC, can be used. There are four primary methods of metal transfer in MIG/MAG, called globular, short circuiting, spray and pulse-spray, each of which has distinct properties and corresponding advantages and limitations.
Originally developed for welding and other non-ferrous materials in the 1940s, MIG/MAG was soon applied to steels because it allowed for lower welding time compared to other welding processes. The cost of inert gas limited its use in steels until several years later, when the use of semi-inert gases such as carbon dioxide became common. Further developments during the 1950s and 1960s gave the process more versatility and as a result it became a highly used industrial process.