Welding as an assembly process has become increasingly more attractive to designers of space structures because of its sufficient strength, endurance, reliability during their service lives, and ease of repair. This article reviews a variety of applications for welding in space and low-gravity environments and describes the unique aspects of the space environment. It compares the applicable welding processes, namely, electron-beam welding, laser-beam welding, and gas-tungsten arc welding and examines the metallurgy of low-gravity welds. Steps taken to ensure the continued development of welding technology in space are also discussed.