G Protein-Coupled Receptors, Part A, Volume 193 in the Progress in Molecular Biology and Translational Science series, highlights new advances in the field. G protein-coupled receptors (GPCRs) represent the largest class of cell surface proteins with an intricate involvement of nearly every physiological process in our body. Approximately, one third of the clinically prescribed medicines target GPCRs and the quest to improve the exiting GPCR-targeting therapeutics continues. These two volumes are focused on activation, signaling and regulation of GPCRs with specific examples of receptor systems and cellular processes.