In the treatment of health related dysfunctions, it is desirable that the drug reaches its site of action at a particular concentration and that this therapeutic dose range remains constant over a sufficiently long period of time to alter the process. However, the action of pharmaceutical agents is limited by various factors, including their degradation, their interaction with other cells, and their incapacity to penetrate tissues as a result of their chemical nature. For these reasons, new formulations are being studied to achieve a greater pharmacological response; among these, polymeric systems of drug carriers are of high interest. These systems are an appropriate tool for time- and distribution-controlled drug delivery. The mechanisms involved in controlled release require polymers with a variety of physicochemical properties. Thus, several types of polymers have been tested as potential drug delivery systems, including nano- and micro-particles, dendrimers, nano- and micro-spheres, capsosomes, and micelles. In all these systems, drugs can be encapsulated or conjugated in polymer matrices. These polymeric systems have been used for a range of treatments for antineoplastic activity, bacterial infections and inflammatory processes, in addition to vaccines.