A review of solutions involving plasma optical spectroscopy applied to on-line welding quality monitoring is presented in this paper. After a brief introduction to welding processes and their requirements in terms of quality monitoring, different proposals for on-line monitoring will be addressed. The basics of welding monitoring via plasma spectroscopy in terms of light capture and hardware and processing requirements will be also introduced, and different approaches will be presented. Finally, a variety of examples regarding field trials in different sectors will be also discussed
