Abstract: The technique of CID MS/MS is rapidly emerging as a useful analytical tool both forstructural identification of complex mixtures and for the analysis of compounds whichare difficult to analyze by gas or liquid chromatography. The applications of MS/MS canbe broadly classified in three areas: fundamental studies, mechanistic studies, and mix-ture analysis. The principle, instrumentaton and applications of MS/MS, and the recentdevelopments are described in this report. (This paper will be publish in two inetolments)