Oral route has been the most popular and successfully route for controlled delivery of drugs because of the flexibility in the designing of dosage form than other routes. The primary objective of controlled drug delivery is to ensure safety and improve efficacy of drug as well as patients compliance through better control of plasma drug level and less frequent dosing. "An ideal controlled drug delivery system is the one which delivers the drug at a predetermined rate, locally or systemically, specific period of time". In the book different mechanistic aspects for design of oral controlled release drug delivery systems such as matrix, reservoir, osmotic pressure, ion exchange resins, altered density etc are given. This book contains brief review on currently existing oral controlled drug delivery system, various formulation approaches and also cover the regulatory consideration of oral controlled drug delivery system.