This book deals with the electron density distribution in molecules and solids as obtained experimentally by X-ray diffraction. It is a comprehensive treatment of the methods involved, and the interpretation of the experimental results in terms of chemical bonding and intermolecular interactions. Inorganic and organic solids as well as metals are covered in the chapters dealing with specific systems. Encompassing a broad interface with other physical sciences this book will appeal to researchers in crystallography and chemical physics.