The field of gas phase ion chemistry has undergone spectac­ ular growth and development in the last decade. Ne\·! experimental techniques have developed and theoretical advancements in quantum chemistry and chemical dynamics have begun to provide quantitative information, deeper insights and important guideposts for experi­ ments. The growing interaction between theoreticians and experi­ mentalists is yielding scientific information of both basic and applied significance. The NATO Advanced Study Institute on Chemistry of Ions in the Gas Phase held at VimeirCl, Portugal, from 6 to 17 September 1982 took place four years after the 1978 Advanced Study Insti­ tute on Kinetics of Ion-Molecule Reactions held at la Baule, France. New theoretical approaches and experimental techniques developed since then are included in this book. Fundamental aspects concerning the kinetics and dynamics of formation and decomposition of gaseous positive and negative ions, their structural charActerisation, energetics and thermochemistry are also discussed. In addition, some recent innovative developments in the areas of photodissociation, multiphoton ionisation, photo­ electron-photoion coincidence spectroscopy, selected ion flow tube technique, and other techniques will be fonnd. The success of the NATO Advanced Institute on Chemistry of Ions in the Gas Phase was mostly due to the high quality of the lectures, panel sessions, research review contributions and the ensuing important discussions which would informally continue after the scheduled sessions. All the participants were ulti­ mately responsible for the attainment of the aims of the Institute.