The structural information collected by X-ray (or neutron) diffraction studies of metallic, ionic, molecular and macromolecular crystals has increased beyond any previously imagined limit. Data are presently compiled in computer-based crystal structure databases. Making particular reference to molecular crystals, it is shown that the information collected may possess a great heuristic value, that is a great potential for guiding the discovery of new chemical facts or the formulation of new chemical theories, provided systematic methods of database analysis and crystal structure interpretation are made available. It is suggested that such methods consist of systematic correlations of structural data pertaining to single molecular fragments as found in many different crystal structures and can be collectively called (crystal) structure correlation methods (SCMs).SCMs are based on the search for and recognition of correlations among the geometrical descriptors of the fragment (structural correlations) and other physical properties of the fragment itself or of the molecule the fragment belongs to (structure-properties correlations).