Thermodynamics of Solutions : From Gases to Pharmaceutics to Proteins This book consists of a number of papers regarding the thermodynamics and structure of multicomponent systems that we have published during the last decade. Even though they involve different topics and different systems they have something in common which can be considered as the signature of the present book. First these papers are concerned with difficult or very nonideal systems i. e. systems with very strong interactions (e. g. hyd gen bonding) between components or systems with large differences in the partial molar v umes of the components (e. g. the aqueous solutions of proteins) or systems that are far from normal conditions (e. g. critical or near critical mixtures). Second the conventional th modynamic methods are not sufficient for the accurate treatment of these mixtures. Last but not least these systems are of interest for the pharmaceutical biomedical and related ind tries. In order to meet the thermodynamic challenges involved in these complex mixtures we employed a variety of traditional methods but also new methods such as the fluctuation t ory of Kirkwood and Buff and ab initio quantum mechanical techniques. The Kirkwood Buff (KB) theory is a rigorous formalism which is free of any of the proximations usually used in the thermodynamic treatment of multicomponent systems. This theory appears to be very fruitful when applied to the above mentioned difficult systems. Eli Ruckensteinhas won many notable awards including the Foundes Award from the American Institue of Chemical Engineers the National Academy of Engineering Founders Award and theNational Medal of Science.His interests includetransport phenomena catalysis colloids and interfces phase transformations thermodynamics and materials. Thermodynamics of Solutions is a collection of papers published by Eli Ruckenstein and Ivan Shulgin concerning a broad spectrum of scientific topics regarding supercritical fluids drugs proteins and other molecules of biomedical or environmental significance. The authors have collected and organized these papers into sections and composed an introduction for each section. This book will be of interest to researchers working in chemical pharmaceutical biomedical and environmental sciences.