Intrinsically disordered proteins (IDPs) are predicted to represent a significant fraction of all functional proteins. Their inherent plasticity allows them to sample more efficiently their surroundings and thereby increase the probability of interaction with one or several different biological partners. Due to their high flexibility, IDPs cannot be represented by a single, three-dimensional structure; rather, an ensemble description can be invoked, where the protein is assumed to interconvert between different conformations. This chapter focuses on the use of NMR spectroscopy to characterize the dynamic behavior of IDPs, in particular residual dipolar couplings, that provide highly sensitive tools for the study of intrinsic structural propensity and conformational transitions accompanying protein function.