Poly(α-hydroxy acids) are important biodegradable polymers with wide applications. Recently O-carboxyanhydrides (OCAs) have emerged as promising monomer equivalents of lactides to synthesize poly(α-hydroxy acids). We will highlight recent advances in controlled ring-opening polymerization of OCAs catalyzed by organocatalysts, enzymes, or organometallic complexes.1 Introduction2 Organocatalysts for O-Carboxyanhydride Polymerization2.1 Synthesis of O-Carboxyanhydride Monomers2.2 Ring-Opening Polymerization of O-Carboxyanhydrides Catalyzed by 4-Dimethylaminopyridine2.3 Epimerization in the Ring-Opening Polymerization of O-Carboxyanhydrides Catalyzed by the Pyridine Base2.4 N-Heterocyclic Carbenes for Ring-Opening Polymerization of O-Carboxyanhydrides3 Enzymes for O-Carboxyanhydride Polymerization4 Organometallic Catalysts for O-Carboxyanhydride Polymerization4.1 Early Efforts4.2 Ring-Opening Polymerization Catalyzed by Zn Complexes4.3 Photoredox Ring-Opening Polymerization Catalyzed by Zn/Ni Complexes5 Conclusion and Perspective