Cytochromes are proteins that catalyze electron transfer reactions of many metabolic pathways. They are involved in drug metabolism and thus determines the therapeutic safety and efficacy of drugs in patients. Cytochrome P450 in mitochondria accounts for 90% of the oxidative metabolism of clinically used drugs during phase 1 reaction. CYP2D6 is a major gene member of this superfamily as it carries out metabolism of 25% of drugs currently available in the market. Contrary to the concept of specificity of enzyme action these can metabolize substrates of different chemistry. Since its discovery, many have intensively studied this unique hemoprotein and contributed to the elucidation of its molecular properties and physiological functions and also the structure-activity relationships of its substrates and inhibitors. Its activity ranges considerably within a population due to genetic polymorphisms which lead to varied responses to drug intake. Studying such polymorphisms which cause a significant impact in the management of patients and helps to achieve the final target of personalizing medicine. This review briefs about history, structure, and function, molecular genetics, substrates, regulators and inhibitors of CYP2D6 and its clinical pharmacogenomics.