The possibilities of NMR spectroscopy in studies of interactions in polymer systems are demonstrated on the example of two types of macromolecular complexes: (i) By measuring H-1 NMR high resolution line intensities, the formation of ordered associated structures of syndiotactic (s) poly(methyl methacrylate)(PMMA) in mixed solvents was quantitatively characterized. The obtained results permit us to assume that the mechanism by which the solvent affects self-association of s-PMMA involves specific interactions of the solvent molecules with PMMA units. Solid state high resolution C-13 NMR spectra of associated s-PMMA gels were also measured and compared with the spectra of a solid s-PMMA sample. (ii) By using C-13 solid state NMR spectroscopy, the differences in the structure of the amorphous and crystalline phases in pure poly(ethylene oxide) and its complexes with p-dichlorobenzene or p-nitrophenol were characterized. Prounounced differences also in the dynamic structure of the crystalline phase in these systems are indicated by the relaxation times T1(C), T1rho(C) and T1rho(H).