Nowadays, pharmaceutical technology and research for new drugs and formulations is of great importance, as scientists attempt to discover even more revolutionary and efficient methods to treat various diseases. At the same time the correct dosing and site targeting are equally important for clinical success. Research in sustained drug release systems is very promising towards such a direction, while it offers advantages and potential rewards contrary to traditional therapy. The drug plasma concentrations remain inside the therapeutic range for a longer time period compared to the conventional formulations. In addition, sustained release formulations may increase the likelihood for the patient to respond to the therapy, since drug formulations are generally characterized by one daily given dose. The rate at which a drug is released from a sustained-release formulation depends upon many factors, while excipients play the most important role. Most sustained release formulations are based on biodegradable polymers in the form of a drug-encapsulating matrix or membrane. Examples range from monolithic devices, polymer-coated capsules and implant devices, hydrogels, to injectable systems based on suspensions of micro-, nanospheres or polymer solutions. The advantages and disadvantages of these different formulation systems are being extensively discussed in the present review.