Synthetic biopolymers (especially the biodegradable polymers) have been extensively researched for their applications in targeted and controlled release (CR) of different therapeutic agents. These synthetic polymers, including (but not limited to) polylactide-polyglycolide copolymers, polyacrylates and polycaprolactones, are being increasingly used in the formulation of novel microparticulate and nanoparticulate delivery systems. The applicability of microparticles and nanoparticles based on these synthetic biopolymers in protein, drug, vaccine delivery and gene therapy is rapidly expanding. In this chapter, we have focused on this novel synthetic biopolymer technology as it relates to the delivery of genes and therapeutic proteins: the syntheses and characterization of the particles, encapsulation or loading of therapeutic agents, protein/gene stability, release and expression. The toxic and safety issues in connection with use of these synthetic biopolymers and the potential usefulness of this delivery system are also discussed.