Welders permanently join pieces of metal by applying heat, using filler metal or fusion process. They join parts being manufactured, build structures and repair damaged or worn parts. They also fabricate parts, tools, machines and equipment used in the construction and manufacturing industries.

Welders may specialize in certain types of welding such as custom fabrication, ship building and repair, aerospace, pressure vessel, pipeline, structural welding, and machinery and equipment repair.

They work for employers such as fabrication shops, steel and platform manufacturers, petrochemical refineries, mechanical contractors, transportation contractors (heavy machinery, aircraft, shipbuilding), and specialized welding shops. They can also be self-employed. Their work may be performed outdoors or indoors, and travel may be required to jobs in remote locations.

Welders require attributes such as good mechanical ability, manual dexterity, good vision, excellent eye-hand coordination, the ability to concentrate on detail work and work as part of a team. They also require the ability to work quickly and accurately, to visualize a finished product, to reason logically and to understand metallurgy.

Occupational hazards in this trade include: sparks, gases, hazardous fumes, burns, heavy lifting, exposure to ultra-violet light and infra-red rays, working at heights, in confined spaces and in trenches.

With experience, welders may advance to positions such as welding inspector, lead hand or welding supervisor. Some welders open their own repair shops or work as rig welders, contracting out their services.