<p>GPCRs function as receptors for various neurotransmitters and hormones, and >30% of current drugs target GPCRs. Although substantial number of GPCR crystal structures have become available, information about GPCR features can only be partially derived from the crystallography data. NMR methods provide information about dynamics of GPCRs over a wide range of frequencies in aqueous media at near-physiological temperature, with minimal modification of the wild-type GPCR covalent structures. Here we review our recent NMR studies of the function-related conformational equilibria of GPCRs, including β<sub>2</sub> adrenergic receptor and μ opioid receptor.</p>