Prodrugs are a class of drug derivatives with little or no pharmacological activity that are converted in vivo to therapeutically active compounds. The primary utility of a prodrug approach is to improve pharmaceutical properties. Because it does not alter the primary structure of the parent drug, the synthesis of prodrugs is usually much less difficult than the synthesis of analogs. The derived physicochemical properties of the resulting derivatives can be carefully tailored by means of structural modification of the promoiety. However, sufficient levels of intrinsic activity of the parent drug need to be assured through in vivo cleavage of the prodrug. The prodrug approach has been successfully applied to a wide variety of drugs. This article briefly discusses advances in strategies for development of prodrugs and their mechanisms of drug release.