TIG= tungsten,inert,gas.you use a small electic torch in one hand and feed wire into the molten puddle with the other hand.Mig welding feeds the wire mechaniclly right thru the torch.Tig offers a much more controlable weld.You use a foot pedal to regulate the amperage and only add as much wire as you want...with mig, you set the amperage and wire feed speed and pull the trigger and what you had set is what you get