Molecular systems are assemblies of molecules designed to possess special qualities and desired functionality. Such systems are important because they provide materials with novel properties, and they will be particularly useful for minimizing electronic devices. Molecular systems often form organized molecular crystals, polymers, or thin films that are significantly more complex than current materials. To provide a sound basis for understanding these levels of complexity, this book provides an analysis of the fundamentals of electronic structures, dynamic processes in condensed phases, and the unique properties of organic molecular solids and the environmental effects on these properties. Also covered are the latest methods in physical chemistry that are particularly useful for deriving and controlling the functionality of molecular systems. A second volume subtitled From Molecular Systems to Molecular Devices is also being published.