β blockers are among the most prescribed drugs in the world. They are registered for a wide range of indications including hypertension, angina pectoris, arrhythmias, heart failure and as secondary prevention after myocardial infection (MI). The purpose of this article is to provide a brief outline of Drug Receptor Interaction, Signal transduction mechanisms and main groups of adrenergic receptors. Besides this it envisages the prevalent β Blockers in market & their side effects and mechanism of action of β blockers.