Adrenergic Receptors (Adrenoceptors) are seven transmembrane proteins belonging to the superfamily of GPCRs. They respond to the endogenous ligands adrenaline and noradrenaline by inducing a cascade of physiological effects. These receptors have a central role in blood pressure and smooth muscle relaxation and heart contraction. After Rhodopsin, they have become the most studied GPCR to date and are targets for the continuous development of agonists/antagonists.