Upset welding (UW) is a resistance welding process utilizing both heat and deformation to form a weld. A wide variety of shapes and materials can be joined using upset welding in either a single-pulse or continuous mode. This article discusses the advantages and disadvantages of upset welding, as well as the types of welds. The advantages include speed, ease of control, fewer defects, enhanced weld properties, simplicity of equipment, less-strict composition requirements, and ability to join difficult-to-weld materials. The article reviews the role of a homopolar generator as an alternative method for supplying the electrical current for upset welding.