A number of accurate diffraction studies are discussed which have yielded information of theoretical chemical interest. The information is two-fold: accurate atomic parameters can be obtained and compared with theoretical calculations through bond length-bond order curves and through analysis of molecular geometry. In addition, more direct information on chemical bonding can be obtained from combined X-ray and neutron diffraction analyses. The experimental charge density obtained in this way can be compared with theory without use of empirical correlation curves. It is concluded that accurate diffraction data have a potential for the study of chemical bonding which is as yet largely unexplored.