Transdermal drug delivery system (TDDS) provides a means to sustain drug release as well as reduce the intensity of action and thus reduce the side effects associated with its oral therapy. Transdermal drugs are self-contained, discrete dosage form . It delivers a drug through intact skin at a controlled rate into the systemic circulation. Delivery rate is controlled by the skin or membrane in the delivery system .A sophisticated complex drug delivery system difficult to formulate. It requires specialized manufacturing process/equipment. Formulated to meet specific biopharmaceutical and functional characteristics. The materials of construction, configuration and combination of the drug with the proper cosolvent, excipient, penetration enhancer, and membrane are carefully selected and matched to optimize adhesive properties and drug delivery requirements. Transdermal drug delivery - an approach used to deliver drugs through the skin for therapeutic use as an alternative to oral, intravascular, subcutaneous and transmucosal routes. Various transdermal drug delivery technologies are described including the use of suitable formulations, carriers and penetration enhancers. The most commonly used transdermal system is the skin patch using various types of technologies. Transdermal technologies may be applied for several categories of pharmaceuticals used for the treatment of disorders of the skin or for systemic effect to treat diseases of other organs. Several transdermal products and applications include hormone replacement therapy, management of pain, angina pectoris, smoking cessation and neurological disorders such as Parkinson's disease. Formulated to deliver the drug at optimized rate into the systemic circulation should adhere to the skin for the expected duration should not cause any skin irritation and/or sensitization ,Enhancing bioavailability via bypassing first pass metabolism ,Minimizing pharmaco-kinetic peaks and troughs , Improving tolerability and dosing Increasing patient compliance in Continuous delivery. © 2010 Elsevier B.V., All rights reserved.