In the third millennium, the emergence of biodegradable and absorbable polymers has markedly advanced drug delivery and tissue engineering fields. Basically, an ideally biopolymer should possess the highest cytocompatibility and genocompatibility, that also should also incorporate methods of fabrication allowing control on its structure and morphology. So far, a number of bioresorbable materials have been investigated as drug delivery systems and scaffolds for tissue engineering/repair. Of these biopolymers, polyesteric polymers(PLA, PGA and their copolymers) appear to provide a biocompatible platform for both in vitro and in vivo applications. In the current chapter, we will review the importance of polyesters as bioscaffolds and drug delivery systems as well as methods for nano/micro particles fabrications. We also provide some information upon genocompatibility and toxicogenomics of cationic polymers in comparison with polyester copolymer PLGA which is now considered as one of the safest synthetic biopolymers, while its surface modification and conjugation with targeting moieties are believed to open new doors towards advanced functionalized bioscaffolds/delivery systems.