The review explores the factors underlying multimetallic cooperativity in the ring-opening polymerization (ROP) of cyclic esters and ethers, focusing on the development of highly efficient multimetallic catalysts. Multimetallic catalysts often outperform monometallic analogues in terms of reactivity and polymerization control, but the origins of this cooperativity are often unclear. Key factors affecting catalyst performance include metal–metal distances, ligand flexibility, electronics, and conformation. The review discusses emerging trends and mechanisms that explain why cooperativity occurs and how to harness it for the development of efficient multimetallic catalysts. It highlights the importance of metal–metal distances, with an optimal "Goldilocks" scenario required for the most efficient catalysis. Ligand flexibility, lability, steric effects, and electronic properties also significantly impact catalyst performance. Mechanistically, multimetallic catalysts often follow a coordination-insertion pathway, but the specific mechanism varies depending on the catalyst structure and nucleophilicity. The review also covers homotrimetallic and homotetrametallic systems, which have shown enhanced activity and stereocontrol compared to monometallic and bimetallic analogues. Heterometallic complexes, combining different metals, have shown superior activity in ROP, potentially due to the ability to tailor specific roles for each metal. Overall, the review provides insights into the structure-activity relationships and mechanisms of multimetallic catalysts, highlighting the potential for further advancements in catalyst design for sustainable polymer synthesis.The review explores the factors underlying multimetallic cooperativity in the ring-opening polymerization (ROP) of cyclic esters and ethers, focusing on the development of highly efficient multimetallic catalysts. Multimetallic catalysts often outperform monometallic analogues in terms of reactivity and polymerization control, but the origins of this cooperativity are often unclear. Key factors affecting catalyst performance include metal–metal distances, ligand flexibility, electronics, and conformation. The review discusses emerging trends and mechanisms that explain why cooperativity occurs and how to harness it for the development of efficient multimetallic catalysts. It highlights the importance of metal–metal distances, with an optimal "Goldilocks" scenario required for the most efficient catalysis. Ligand flexibility, lability, steric effects, and electronic properties also significantly impact catalyst performance. Mechanistically, multimetallic catalysts often follow a coordination-insertion pathway, but the specific mechanism varies depending on the catalyst structure and nucleophilicity. The review also covers homotrimetallic and homotetrametallic systems, which have shown enhanced activity and stereocontrol compared to monometallic and bimetallic analogues. Heterometallic complexes, combining different metals, have shown superior activity in ROP, potentially due to the ability to tailor specific roles for each metal. Overall, the review provides insights into the structure-activity relationships and mechanisms of multimetallic catalysts, highlighting the potential for further advancements in catalyst design for sustainable polymer synthesis.