The recent trends in the synthesis of functional poly(ester)s by ring-opening polymerization (ROP) are reviewed. While the use of ROP processes for the synthesis of poly(lactide), poly(lactide-co-glycolide) and several poly(lactone)s has been well studied, the paucity of functional groups available for further reaction limits their application. Recent efforts to expand this available functionality are reviewed focusing on the application of renewable resources in the synthesis of new monomers and the utilization of click chemistry to provide common intermediate polymers in the manipulation of poly(ester) functionality. In turn these advances are leading to a new generation of precisely controlled nanoparticles comprised entirely of poly(ester)s.