Introduction and historical background

Chapter 1 provides an introduction to the subject of polymorphism in molecular crystals, including definitions, terminology, nomenclature, and historical development of the subject since the first recognition of the phenomenon in 1823. Topics covered include the difficulty in establishing a database for statistical study of polymorphism, the frequency of occurrence of polymorphism, the literature sources of polymorphic compounds, and literature sources of examples of polymorphism, that is, Cambridge Structural Database, Powder Diffraction File, the patent literature, and the scientific literature. Statistics on crystal polymorphism among the elements in inorganic compounds and macromolecular (i.e., biological) molecules precede the historical perspective. The chapter closes with a brief survey of the commercial importance of polymorphism.