NMR spectroscopy is a powerful approach for quantitating molecular conformational dynamics at multiple atomic sites and over multiple time scales. Extensive studies by solution and solid-state NMR spectroscopy of spin relaxation and line shapes in biological macromolecules have been performed in order to characterize the amplitudes, time scales, and energetics of intramolecular conformational modes and to elucidate the relationships between conformational dynamics, structure, and function. This review describes NMR spectroscopic methods for investigation of conformational dynamics together with theoretical descriptions appropriate for interpretation and simulation of the techniques, surveys the range of results available from solution and solid state NMR studies of proteins and other biomolecules, and identifies opportunities for further individual and collaborative development of solution and solid state NMR techniques for characterizing the dynamical properties of biological macromolecules.