Intermolecular forces determine the structure and physical properties of molecular solids and liquids, and play a major role in many biochemical processes, such as drug receptor binding. We are exploiting recent advances in the theory of intermolecular forces to derive highly accurate model intermolecular potentials from the ab initio wavefunctions of the molecules. The novel feature of these anisotropic atom-atom potentials is that they automatically represent the effects of lone pair and pi electron density on the orientation dependence of hydrogen bonding and pi - pi interactions reliably. The resulting model potentials are more realistic, and mathematicallysophisticated, than the isotropic atom-atom potentials that are generally used in molecular modelling. These methods led to the successful prediction of the crystal structure of C6H2Br2ClF and of a high-pressure phase of pyridine. The non-empirical intermolecular potentials can be used to model the organic solid state using the code DMACRYS, which has been developed by the Price group and licensed through UCLB.