The Glow Discharge Optical Emission Spectrometer (GD-OES) is used for matrix and surface analysis. With cathodic sputtering in an argon plasma, sample material is removed from the surface very uniformly; mono-layer per mono-layer. The sputtered atoms are excited in the glow discharge plasma. The resulting emission spectra is analysed by a multichannel spectrometer, making it possible to analyse up to 58 elements simultaneously. The intensity of the emitted light is proportional to the concentration of the element. The very high sputtering rates that are obtained with this techniques makes analysis very fast (a few seconds to only a few minutes), with the result that a big throughput of samples can be achieved. It finds wide application in the analysis of metals, alloys, stainless steels, aluminium, copper, brass, etc. Calibrations are achieved by analysing Certified Reference Standards (CRM'S). It has a wide linearity over wide concentration ranges. With the additional function of radio-frequency plasma, non-conducting samples can also be analysed. When the intensity of the emission lines is recorded as a function of the sputtering time, a depth profile is obtained. This depth profile is used to study surface phenomena of materials.