The conventional oral dosage forms has significant drawbacks of low bioavailability due to hepatic first pass metabolism and tendency to produce rapid blood level spikes (Both high and low), leading to a need for frequent dosing, which can be both cost ineffective and inconvenient. To improve such characters transdermal drug delivery system (TDDS) was emerged which will improve the therapeutic efficacy and safety of drugs by more precise (i.e. site specific) placement within the body thereby reducing both the size and number of doses. The TDDS has numerous advantages over the more traditional drug delivery system. These include high bioavailability, absence of first pass hepatic metabolism, maintenance of steady plasma level of the drug, increase therapeutic efficiency. This review article provides an overview of TDDS, its advantages over conventional dosage forms, Limitations, various components of Transdermal patches, types of Transdermal patches, methods of preparation and Ideal requirements for TDDS, regulatory issues over transdermal drug delivery and its physicochemical methods of evaluation. Key words: Transdermal drug delivery systems, Transdermal patches, skin penetration, Topical drug delivery