The International Union of Basic and Clinical Pharmacology (IUPHAR) / British Pharmacological Society (BPS) Guide to PHARMACOLOGY is an expert-curated resource of ligand-activity-target relationships, the majority of which come from high-quality pharmacological and medicinal chemistry literature. It is intended as a “one-stop shop” portal to pharmacological information and its main aim is to provide a searchable database with quantitative information on drug targets and the prescription medicines and experimental drugs that act on them. In future versions we plan to add resources for education and training in pharmacological principles and techniques along with research guidelines and overviews of key topics. We hope that the IUPHAR/BPS Guide to PHARMACOLOGY (abbreviated as GtoPdb) will be useful for researchers and students in pharmacology and drug discovery and provide the general public with accurate information on the basic science underlying drug action.