The preparation of stable thin films of controlled structure, composition, and thickness is a discipline bridging vacuum and materials sciences which has had significant effect on optics and electronics, although providing a limited number of working thin‐film substances. Techniques continue to be studied to extend the range of usable film materials on which thin‐film devices often depend for their development. Increasing use has been made in thin‐film technology of physical and chemical phenomena occurring in low‐pressure plasmas which are convenientinsitusources of activated gas and energetic ions to be applied as additional agents in film growth mechanisms. Thus ion extraction from plasmas for uniform doping during film growth is more likely to find wide use than ion implantation of solids. Energetic ions and/or activated species in ionized gas are now employed in processes forsurfacetreatment(nitriding),deposition(sputtering, ’’ion plating,’’ activated evaporation, plasma polymerization), and also foretching(sputtering, plasma etching). Although processes exist in which both physical and chemical effects are recognized to occur, treatment of the process mechanisms tends to be divided between two schools—one concerned withphysicaleffects such as ion impact sputtering and implantation, and the other withchemicaleffects arising from the release of reactive species in plasma‐activated gases. Experiments are described which show that the inner walls of a plasma reaction vessel acquire in the electrode region a negative potential to the plasma in excess of the floating value related to the random electron energy. Ions and electrons are accelerated in the positive ion sheaths which form at the walls of the vessel confining the plasma. Some recent experiments are described which demonstrate how reactive and energetic plasma components can interact. These studies show that (i) gaseous reaction products are more rapidly released from carbon in an O2‐plasma by ion impact, (ii) prevention of polymer growth on a surface by sputtering in a fluorocarbon gas plasma exposes the surface to more rapid attack by fluorine radicals, and (iii) energetic ion bombardment of degraded material during deposition on a target in a hydrocarbon gas plasma results in the growth of a carbon rich layer of unusual structure and properties.