β-Adrenoceptors (β1, β2, β3) are G protein-coupled receptors expressed in both central and peripheral sites and are activated either by norepinephrine released from symphathetic terminals or by epinephrine released from the adrenal medulla. Most β-adrenoceptor-mediated actions involve stimulation of intracellular adenylate cyclase and lead to relaxation of vascular, urogenital and bronchial smooth muscle, stimulation of cardiac rate and force, stimulation of rennin secretion, and stimulation of insulin and glucagons secretion. Besides its function in cardiac stimulation, β2 adrenoceptors play a major role in bronchodilation and are a good target for asthma and chronic obstructive pulmonary disease.