Welding is one of the most common and dependable methods of joining metal parts such as airplanes, autos, household appliances, barges, buildings, storage tanks, and tugs. There are more than ninety-eight different welding processes; however, most of these fall under three major types - gas, arc, and resistance - all of which are manual, semi-automatic, or automatic.

Welders are classified as semi-skilled or skilled. Semi-skilled welders usually perform repetitive work which does not, as a rule, involve critical thinking and strength requirements. The skilled welder is able to plan, layout, and work from drawings or other specifications to meet specified requirements using any one or all of the welding processes. A working knowledge of the welding properties of steel, stainless steel, cast iron, brass, bronze, aluminum, nickel, along with other alloys is necessary. An experienced welder may qualify as a welding technician, supervisor, inspector, or foreman.