Sustained release drug system is any drug or dosage form modification that prolongs the therapeutic activity of the drug. Ideally a sustained release oral dosage form is designed to release rapidly some predetermined fraction of the total dose in to GI tract. This fraction (loading dose) is an amount of drug, which will produce the desired pharmacological response as promptly as possible and the remaining fraction of the total dose (maintenance dose) is then release at a constant rate. The rate of the drug absorption from the entire maintenance dose into the body should equal to the rate of the drug removal from the body by all the processes over the time for which the desired intensity of pharmacological response is required. We sincerely hope that this book will helpful to student as well as industry and academic professionals involved in pharmaceutical and other related science.