G protein-coupled receptors (GPCRs) are the largest family of proteins involved in signal transduction across membranes and one of the most important pharmaceutical drug target classes. In the past five years, an unprecedented number of X-ray structures of GPCRs have been solved, affording us first peeks at the molecular details of their function. Based on these and forthcoming structures, this COST Action will bring together experts in a wide range of complementary methods to unravel details of the activation mechanism, ligand binding, and the effect of the membrane and other interaction partners on GPCRs. The information exchange that will be made possible by the COST Action will lead to innovative insights into mechanistic details of GPCR function. This will in turn give rise to novel effector molecules to be used as lead structures for drug development, offering valuable new opportunities for European pharmaceutical research and industry.