NMR spectroscopy allows for the determination of high resolution structures, as well as being an efficient method for studying the dynamics of protein-protein and protein-peptide complexes. ¹⁵N relaxation and H/D exchange experiments allow for the analysis of these structural dynamics at a residue specific level. Calmodulin (CaM) is a small cytosolic Ca²⁺ binding protein that serves as a control element for many enzymes. An important target of CaM are the nitric oxide synthase (NOS) enzymes that play a major role in a number of key physiological and pathological processes. Studies have shown CaM facilitates a conformational shift in NOS allowing for efficient electron transfer through a process thought to be highly dynamic and at least in part controlled by several possible phosphorylation sites. This review highlights recent work performed on the CaM-NOS complexes using NMR spectroscopy and shows remarkable differences in the dynamic properties of CaM-NOS complexes at physiologically relevant Ca²⁺ concentrations. It also shows key structural changes that affect the activity of NOS when interacting with apoCaM mutants and NOS posttranslational modifications are present.