G-protein-coupled receptors (GPCRs) transduce physiological and sensory stimuli into appropriate cellular responses and mediate the actions of one-third of drugs. GPCR structural studies have revealed the general bases of receptor activation, signaling, drug action and allosteric modulation, but so far cover only 13% of nonolfactory receptors. We broadly surveyed the receptor modifications/engineering and methods used to produce all available GPCR crystal and cryo-electron microscopy (cryo-EM) structures, and present an interactive resource integrated in GPCRdb ( http://www.gpcrdb.org ) to assist users in designing constructs and browsing appropriate experimental conditions for structure studies.