This review surveys recent investigations of conformational fluctuations of proteins in solution using NMR techniques. Advances in experimental methods have provided more accurate means of characterizing fast and slow internal motions as well as overall diffusion. The information obtained from NMR dynamics experiments provides insights into specific structural changes or configurational energetics associated with function. A variety of applications illustrate that studies of protein dynamics provide insights into protein-protein interactions, target recognition, ligand binding, and enzyme function.