The adenosine A receptor (AAR) is one of four adenosine receptor subtypes belonging to the Class A family of G protein-coupled receptors (GPCRs). Until recently, the AAR remained poorly characterised, in part due to its relatively low affinity for the endogenous agonist adenosine and therefore presumed minor physiological significance. However, the substantial increase in extracellular adenosine concentration, the sensitisation of the receptor and the upregulation of AAR expression under conditions of hypoxia and inflammation, suggest the AAR as an exciting therapeutic target in a variety of pathological disease states. Here we discuss the pharmacology of the AAR and outline its role in pathophysiology including ischaemia-reperfusion injury, fibrosis, inflammation and cancer.2B