This book specifically addresses the use of (13)C and (15)N NMR spectroscopy to derive information on the internal motions of proteins and peptides in solution. Basic methods of NMR relaxation, along with the general theory of correlation functions and spectral densities, are first covered, followed by in-depth analyses and comparisons of various motional models and molecular dynamics simulations used to derive protein dynamics information from NMR relaxation experiments. Motional model equations are expressed in computer program-ready format. The text is ideally suited for graduate and post-graduate students as well as experienced professionals.