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G proteins are a highly conserved family of membrane‐associated proteins composed of α, β, and γ subunits. The α subunit, which is unique for each G protein, binds GDP or GTP. Receptors such as those for β‐ and α‐adrenergic catecholamines, muscarinic agonists, and the retinal photoreceptor rhodopsin, catalyze the exchange of GDP for GTP binding to the α subunit of a specific G protein. Gα · GTP regulates appropriate effector enzymes such as adenylyl cyclase or the cyclic GMP phosphodiesterase. The βγ‐subunit complex of G proteins is required for efficient receptor‐catalyzed a subunit guanine nucleotide exchange and also functions as an attenuator of α subunit activation of effector enzymes. Recent elucidation of both receptor and G protein primary sequence has allowed structural predictions and new experimental approaches to study the mechanism of receptor‐catalyzed G protein regulation of specific effector systems and the control of cell function including metabolism, secretion, and growth.—Weiss, E. R.; Kelleher, D. J.; Woon, C. W.; Soparkar, S.; Osawa, S.; Heasley, L. E.; Johnson, G. L. Receptor activation of G proteins. FASEB J.2: 2841‐2848; 1988.