The ability of a particular substance to exist in several different crystal forms (unsolvated or solvated) is called polymorphism or solvatomorphism. These phenomena are frequently observed in solid pharmaceuticals. Polymorphs and solvatomorphs of a compoud differ in their physical and biological properties (crystal shape, hardness, melting point, solubility, pharmacokinetics, bioavailability, etc.). This influences commercial drug formulations and their therapeutical effect. The exact theoretical prediction of all polymorphs and solvatomorphs is not yet possible. The most frequently used analytical method of detection and characterization of polymorphic and solvatomorphic forms is X-ray diffraction (single-crystal structure analysis and collection of powder patterns). Producers of original pharmaceuticals endeavour to patent all crystal forms of the developed active substance, while generic producers search for new polymorphs (solvatomorphs) or technologies. Clearly this can cause lawsuits.