The science and technology associated with pharmacy has progressed enormously over the past few decades. Significant advances in the understanding of diseases have necessitated the need to optimize drug therapy. The concern today is not just to produce elegant and accurate dosage forms but also to ensure that optimum amount of drug reaches the target site at an optimal rate and it concentration is maintained for the entire duration of therapy. A thorough background of the fate of drug after its administration; the rate processes to which it is subjected in the body and its behaviour after biotransformation, are thus very essential in addition to the knowledge about its pharmacodynamics. The twin disciplines of Biopharmaceutics and Pharmacokinetics have, therefore, been developed with the objective of learning how drugs can be utilized optimally in the treatment of diseases-through design and development of new and better therapeutic moieties, new dosage forms and appropriate dosage regimens. Significant expansion of the chapter on controlled release medication has been made to cover in a broader perspective, the principles employed in the design of such dosage forms, their classification and brief description of the technologies and products delivered by various routes. The concerted attempt was to collectively address the several modern approaches adopted to design the modified drug delivery systems, which is an exciting and highly dynamic area of pharmaceutical research.