Meeting the demand for the second edition of this book, which is – despite a reprint in 1990 – no longer available, and considering the progress that has been made during the last decade in the study of solvent e¤ects in experimental and theoretical organic chem-istry, this improved third edition is presented to the interested reader. Following the same layout as in the second edition, all topics retained have been brought up to date, with smaller and larger changes and additions on nearly every page. Two Sections ( and ) are completely new, dealing with solvent e¤ects on host/guest complexation equilibria and reactions in biphasic solvent.