The interaction of water at organic surfaces or interfaces is of fundamental and technological interest and importance in chemistry, physics and biology. Progress towards an in-depth, molecular interpretation of the structure and dynamics of interfacial water needs a range of novel experimental and simulation techniques. We are now reaching the stage at which we understand, at the molecular level, the mutual perturbation at a macromolecule/water interface. The aims of this book are to provide with a comprehensive background to the properties of bulk water at the microscopic level and with a substantial account of the theoretical and experimental contributions which have been done to understand the role of water in various systems from some model systems to the more complex ones such as the biological systems.