Most people are familiar with the fact that diamond and graphite are both composed only of carbon; yet they have very different properties which result from the very different structures of the two solids – they are polymorphs of carbon. Understanding the relationship between the structures and the properties of materials is of fundamental importance in developing and producing new materials with improved or new properties. The existence of polymorphic systems allows the direct study of the connection between structures and properties. This book provides grounding on the fundamental structural and energetic basis for polymorphism, the preparation and characterization of polymorphic substances and its importance in the specific areas of pharmaceuticals, pigments and high energy (explosive) materials. The closing chapter describes the intellectual property implications and some of the precedent patent litigations in which polymorphism has played a central role. The book contains over 2500 references to provide a ready entry into the relevant literature.