The monograph contains precise description about the phenomenon of polymorhism and multiple molecules in organic crystals, a subject of immense interest to scientists working in the field of pharmaceuticals,crystal growth, X-ray crystallography and materials scientists, in general. A comprehensive review of literature has been made, covering polymorhic and structural properties of biphenyls. The lead author's research group has conducted crystallographic investigations separately on two different series of substituted biphenyl systems, during the past few years. A comparison of the crystallization process for substituted biphenyls, their X-ray molecular and crystal structures and analysis of the occurrence of multiple molecules in the asymmetric unit cell, is presented in this monograph. This book is an ideal choice for Master's level students pursuing research in X-ray crystallography of small molecules. It will enable them to gain an insight into the fascinating world of polymorphism, crystals and crystallography.The learning design of the book is such that the subject of crystallography is explored in terms of its applicability and not as an abstract collection of concepts.