Over the last 60 years, polyolefin-based plastics have considerably been developed to become the most used materials today. However, they are made from non renewable fossil resources and pose an environmental problem (waste storage, pollution…). As a consequence, biodegradable and biocompatible polymers may be a viable alternative to petrochemical-based plastics. As a result, biodegradable aliphatic polyesters and polycarbonates have received increasing attention over the last years. They can be obtained by the ring-opening polymerization (ROP)of cyclic monomers. In the present book, the synthesis of well-defined and ligand-supported group 13 complexes for use as ROP initiators of cyclic esters and carbonates is described. To this purpose, novel salen- and N,O,N-type ligands have been readily synthesized and coordinated onto group 13 metal centers (Al, Ga). All the complexes have been structurally characterized and successfully tested as initiators in the ROP of rac-lactide, e-caprolactone and trimethylene carbonate, yielding the corresponding biodegradable polyesters/carbonates. This work should be useful to professionals in organometallic and polymer chemistry/catalysis.