The ring-opening polymerization of lactones allows the controlled production of aliphatic polyesters, such as polylactide (PLA) or polycaprolactone (PCL), which are applied as commodity plastics or in medicine. An on-going research interest for our team is to discover high activity and selectivity ring-opening polymerization catalysts, particularly focussing on the production of polylactide. PLA is a bio-renewable polymer; the monomer lactide is harvested from high starch content biomass and PLA is degradable or recyclable after use. Our research into catalyst development focusses on improving activity and control of stereochemistry so as to modulate the thermal-mechanical performance of PLA. Recent research has focussed on phosphasalen ligands and lanthanide complexes, which can be targeted to deliver both high isoselectivity and activity and forming stereoblock PLA.