In metal inert gas (MIG) welding a continuous solid wire electrode and a shielding gas are sent through a welding gun into the weld pool, melting the base metals and forming the join. As the wire is fed from a reel, the welder moves the torch along the joint line. The shielding gas, usually a mixture of carbon, oxygen and CO2, forms the arc plasma, protects the weld from air contamination and helps reduce spatter by transferring molten droplets to the weld pool.

A versatile technique with many applications, MIG welding is fast and its continuous electrode feed allows long weld passes, reducing the number of passes necessary and increasing productivity. It is fairly clean, creating little waste, and is suitable for various different metals. Disadvantages include the higher level of preparation required and the more expensive, less portable equipment needed. The external gas source means welding is more difficult to control outside the workshop, where conditions such as wind can cause problems.