From decades application of the medicaments topically has been rampant to attain a particular therapeutic response and Transdermal Drug Delivery System (TDDS) has been a boon for topical administration of therapeutic substances. These are self-contained, discrete dosage forms offering painless and desired pharmacokinetics. The drugs which are not suitable for administration through oral route due to various inefficiencies can be administered via transdermal route. These are the preparations that vary in sizes, containing the active ingredient to be applied on the unbroken skin to deliver the active pharmaceutical ingredient into the systemic circulation through diffusion process thus avoiding the first pass metabolism. The present review describes the Anatomy of skin, Components, Types, Merits, Demerits, and Evaluation of Transdermal Drug Delivery System.