Abstract: pH Sensitive Drug Delivery Systems (PSDDS) are gaining importance as these systems deliver the drug at specific time as per the pathophysiological need of the disease, resulting in improved patient therapeutic efficacy and compliance. Diseases wherein PSDDS are promising include asthma, peptic ulcer, cardiovascular diseases, cancer and hypertension. The specific time that patients take their medication is very important as it has significant impact on treatment success. Optimal clinical outcome cannot be achieved if drug plasma concentrations are constant. If symptoms of a disease display circadian variation, drug release should also vary over time. Drug pharmacokinetics can also be pH-sensitive; therefore, variations both in a disease state and in drug plasma concentration need to be taken into consideration in developing drug delivery systems intended for the treatment of disease with adequate dose. PSDDS wherein the drug release is controlled primarily by the delivery system, stimuli induced PSDDS in which release is controlled by the stimuli, such as the pH present in the intestinal tract. These systems are useful to several problems encountered during the development of a pharmaceutical dosage form. These, as well as pertinent issues, are addressed in this review.