As materials polymers are almost always used as "solids". A structural and dynamic characterization of the polymers in question is necessary in order to understand the relations between properties and structure and, on the basis of these relations, to design new polymer materials. As is well known, the X-ray diffraction method has contributed to the tructural determination of polymers with high crystallinity. However, most polymers have low crystallinity and so structural information about the noncrystalline region, which is the major component, cannot be obtained by X-ray studies. Therefore, the X-ray diffraction method has a limitation for the structural analysis of such systems. Further, it can be said that chain segments in the noncrystalline region are sometimes in a mobile state, so that he X-ray diffraction method provides no structural or dynamical information. On the other hand, the solid state NMR method provides information about the structure and dynamics of a sample irrespective of whether the region studied is crystalline or noncrystalline.