G-protein-coupled receptors (GPCRs) are essential components of the signalling network throughout the body. To understand the molecular mechanism of G-protein-mediated signalling, solved structures of receptors in inactive conformations and in the active conformation coupled to a G protein are necessary^,. Here we present the structure of the adenosine A_2A receptor (A_2AR) bound to an engineered G protein, mini-G_s, at 3.4 Å resolution. Mini-G_s binds to A_2AR through an extensive interface (1,048 Ų) that is similar, but not identical, to the interface between G_s and the β₂-adrenergic receptor. The transition of the receptor from an agonist-bound active-intermediate state^, to an active G-protein-bound state is characterized by a 14 Å shift of the cytoplasmic end of transmembrane helix 6 (H6) away from the receptor core, slight changes in the positions of the cytoplasmic ends of H5 and H7 and rotamer changes of the amino acid side chains Arg^3.50, Tyr^5.58 and Tyr^7.53. There are no substantial differences in the extracellular half of the receptor around the ligand binding pocket. The A_2AR–mini-G_s structure highlights both the diversity and similarity in G-protein coupling to GPCRs and hints at the potential complexity of the molecular basis for G-protein specificity.