Functionally, proteins are the most important building blocks of life. Their diverse biological activities are often intricately linked to their internal mobility. Model-free analysis of NMR relaxation data is the most widely employed method for experimentally studying protein dynamics at the atomic level. This book investigates all aspects of the model-free data analysis chain, and shows how to obtain a much improved dynamic description of macromolecules. Using statistical model selection the choice of model-free model is overhauled to uncover previously hidden motions, failed model-free models are eliminated, the optimisation of the model-free models is significantly improved to increase the accuracy of the final results and a new protocol is presented for the optimisation of the global model which reverses the current logic thereby solving the hidden motion problem and the issues of artificial chemical exchange and artificial nanosecond motions. The advances presented here should be of interest to anyone studying the internal motions of complex molecules.