We report the synthesis of alternating poly(lactic-co-glycolic acid) via a regioselective ring-opening polymerization of (S)-methyl glycolide. An enantiopure aluminum salen catalyst with binaphthyl backbone facilitates the regioselective ring-opening of this unsymmetrical cyclic diester exclusively at the glycolide acyl-oxygen bond site. This living, chain-growth polymerization is able to reach low dispersities with tailored molecular weights. Quantitative regioselectivity calculations and sequence error analysis have been established for this sequence-controlled polymer.