This book describes the synthesis, characterization, formulation design and in vivo efficacy of novel biodegrdable polymers based on natural fatty acids. Effective drug therapy has maximum therapeutic effect in the desired site of action with minimal adverse effects. When a drug is administered systemically by intravenous, intramuscular or oral dosing, it is distributed in the body to various organs perfused with blood, and only a relatively small amount reaches its target tissue. Locally injected formulation releases the drug at a slow rate for a prolonged period of time while providing high local therapeutic concentrations in the diseased site with minimal body distribution of toxic drugs resulting in less side effects and toxicity. We have developed a biodegradable formulation that can be injected in the tumor and deliver anticancer drugs at the site of action with low systemic exposure and complete degradation in the end of action. This formulation proved to be efficient in several cancer models treated with different anticancer agents.