This article reviews recent developments in the polymerization of ar-amino acid-N-carboxyanhydrides (NCAs) to form polypeptides. Traditional methods used to polymerize these monomers are described, and limitations in the utility of these systems for the preparation of polypeptides with controlled molecular weights and narrow molecular weight distributions are discussed. The development of transition-metal-based initiators, which activate the monomers to form covalent active species, permits the formation of polypeptides via the living polymerization of NCAs. In these systems, polymer molecular weights are controlled by monomer-to-initiator stoichiometry, polydispersities are low, and block copolypeptides can be prepared. The scope and limitations of these initiators and their key features and mode of operation are described in detail in this highlight.