Controlled drug delivery technology represents one of the most rapidly advancing areas of pharmaceutical science. The applications of controlled drug delivery applications include both sustained (over days/weeks/moths/years) delivery and targeted (e.g. to a tumor, diseased and blood vessel) delivery on a one-time or sustained basis. Polymer-based drug delivery systems are used to optimize the therapeutic properties of drugs and render them safer, effective and reliable. Such delivery systems offer numerous advantages compared to conventional dosages forms which include improved efficacy, reduced toxicity, and improved patient compliance and convenience. Generally, all controlled release systems aim to improve the effectiveness of drug therapy. This improvement can increase the therapeutic activity compared to the side effects, reducing the number of drug administrations required during treatment. Moreover, the attached drugs can be targeted to specific organs, tissues or cells. On the other hand, polymeric drugs and macromolecules used as drug carriers can be easily synthesized at low cost, freely water-soluble,non-toxic and non-immunogenic.