The first conference in this series, devoted principally to the interaction of positrons in gases, was held at York University, Toronto, in July 1981 immediately preceding the XII ICPEAC in Gatlinburg, and the proceedings were published in the Canadian Journal of Physics, volume 60 (1982). So successful was this meeting that the decision was taken to hold a second one around the time of XIII ICPEAC in Berlin in 1983. London was clearly a convenient location but, rather than the obvious choice of University College London in central London, the Organising Committee decided that the beautiful and peaceful surroundings of Royal Holloway College would provide a more pleasant and intimate atmosphere for a small meeting. Even a small conference requires substantial sums of money to pay the expenses of invited speakers and when considering possible sources of funds the Organising Committee recognised that the intended format of the meeting and the international composition of the participants made it appropriate to apply to the NATO Science Committee for support under the Advanced Research Workshop Programme. This was one of the few successful applications made this year, and so it was that the conference became the 'NATO Advanced Research Workshop on Positron Scattering in Gases'. The Workshop, with approximately sixty participants, started after lunch on 19 July, 1983 and finished at mid-day on 23 July.

During the last two decades, the theory of ion-atom collisions, and particularly of charge-exchange reactions, has advanced rapidly to the point where existing texts are no longer suitable as an introduction to the subject. This book aims to remedy the situation by providing an account of modern theoretical methods used to study the interaction of positive ions with atoms (or ions), concentrating particularly on charge-exchange reactions. These reactions cannot be studied in isolation, and it is necessary to consider to some extent, the whole range of ion-atom collisions leading to elastic scattering, excitation, and ionization. The material is presented at a level suitable for beginning research students and is self-contained, but assumes a knowledge of undergraduate quantum mechanics and atomic physics. It will also be useful for experimentalists who wish to assess the status of theoretical treatments of those collision processes in which they are interested.