The delivery of drugs from biodegradable polymeric materials for human and animal use has attracted considerable attention of investigators throughout the scientific community. Various types of polymers have been synthesized and tested for this purpose which include: poly(α-esters), poly(aliphatic esters), polyorthoesters, polyphosphazenes, poly(phosphate esters), polymers based on amino acids, natural and synthetic peptides and proteins, polysaccharides and polyanhydrides. Comprehensive reviews on various biodegradable polymers and their advantages have been published [1-5]. This chapter concentrates on the polyanhydride class of polymers. Polyanhydrides are useful bioabsorbable materials for controlled drug delivery. They are hydrolytically unstable and hydrolyze to diacid monomers in contact with body fluids. Since their introduction to the field of controlled drug delivery, about 10 years ago, extensive research has been conducted to study their chemistry as well as their toxicity and medical applications. Several review articles have been published on polyanhydrides and the focus has been on controlled drug delivery applications [1, 2]. A major part of this chapter will review recent developments in the chemistry and properties of polyanhydrides, which includes new synthetic methods, new polymeric structures, and in depth characterization of polyanhydrides. The degradation and drug release properties and applications that were not reviewed previously are included. A review article by the same authors concentrating on polyanhydride applications and toxicity is in preparation .