This chapter discusses nuclear magnetic resonance (NMR) spectroscopy of polymers. The NMR phenomenon makes it possible to detect transitions of the magnetic nuclei between the spin states. In general, spin-lattice relaxation, through molecular motions, effects NMR signal intensities, while spin-spin relaxation is reflected in the broadening of NMR signals. The resonant frequency of a nucleus depends on its chemical and/or structural environment in addition to its nuclear characteristics. Nuclei with magnetic moments may be coupled to each other either directly through space (dipolar coupling) or indirectly through their intervening chemical bonds (scalar coupling). NMR serves as a local microscopic probe of polymer microstructures and their motions. As a consequence, NMR can even provide highly resolved spectra for dissolved polymers whose overall motion may be sluggish (high solution viscosities), but whose local segmental motions are rapid. To realize the full potential of 13C NMR in microstructural studies of polymers, the connections between constituent microstructural features and their corresponding effects on chemical shifts must be established. As a result of dipolar interactions with nearby abundant protons, the 13C resonance linewidths observed in rigid organic polymers are typically tens of kHz. Application of high-power 1H-DD and rapid MAS techniques to record the 13C-NMR spectra of solid polymers can produce high-resolution spectra. The applications of solid state NMR to polymer science range from simple solution-like experiments to complex multidimensional experiments are finally discussed in the chapter.