Nuclear magnetic relaxation in organic crystals is strongly influenced by processes of motion, such as the rotation of molecular substituents, the reorientation of molecules in the lattice, and the diffusion of molecules through the lattice. In company with studies of dielectric relaxation, heat capacity, and structure, nuclear magnetic resonance (NMR) experiments are valuable in examining these processes. In this paper, we review some advantages and limitations of the NMR method, and show correlations with other methods of studying molecular motions. NMR studies over a range of temperatures and moderate pressures are described for a variety of organic solids, including long-chainn-alkanes, planar molecules such as benzene, and nearly spherical molecules such as camphor and hexamethylbenzene.