Poly(lactic acid) (PLA) represents the most commercially successful biodegradable synthetic polymer. But to replace petrochemical polymers or to develop advanced materials for new applications, there is an urgent need to modify and improve PLA's physical properties, especially PLA's elasticity, thermal stability, hydrophilicity and degradation rate. One of the most versatile ways to improve PLA's properties is the copolymerization of lactide with lactones, especially e-caprolactone. How copolymerization influences the properties of PLA depends on monomer sequence, with statistical 7 and block copolyesters showing contrasting properties relevant to different applications.