This article is focused on emission spectroscopy whose the main interest is in a non intrusive diagnostics, allowing a control and a piloting of the surface treatment process. To analyse a given plasma process, the emission spectroscopy must be coupled to the plasma kinetic equations. These mechanisms are described for a PVD process with a RF-activated magnetron DC cathode where it is shown how to follow the metal ionization degree with the example of Cu sputtering. In a second part of the article, it is shown how to measure the absolute densities of N- and O-atoms by NO titration in flowing N-2 and O-2 post-discharges, with applications to the activation of elastomers and to the sterilization of oral bacteria. In a chosen N-2-O-2 flowing microwave post-discharge, it has been obtained a decrease of 12 log (when 6 log is necessary for sterilization) for E. coli bacteria after a treatment time of 15 min. (C) 2004 Elsevier B.V. All rights reserved.