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...