The chapters of this volume represent the invited papers delivered at the 3rd International Conference on Multiphoton Processes (ICOMP III) held in Iraklion, Crete, Greece, September 5-11, 1984. The invited papers at a conference like ICOMP cannot possibly cover the whole field which has grown to immense proportions in recent years, overlapping with such diverse areas as atomic and molecular spectroscopy, plasma physics, nonlinear optics, quantum optics, etc. We believe these contributions represent that part of the research activity which has been attracting the most interest in the past year or so, as well as reviews of some of the more established topics. Even within this scope, and given the confines imposed by the fi nite duration of a conference, important and timely topics are inevitably left out. But then, there will be ICOMP IV. The collection of articles in this volume, combined with extensive ref erences to related work given by the authors, should provide an introduc tion to the major problems of the field and its state of the art. The chapters have been arranged according to thematic proximity, beginning with atoms, and continuing on with molecules and surfaces. This classi fication, however, would not cover all the subject matter even within the limited scope of the conference and of this volume.