While there are now many redox-switchable catalysts, mechanistic understanding of how these systems perform redox-switching is not well established. The oxidation state of the catalyst that is the active for catalysis and the efficiency of the redox switch are dependent on many factors. In addition to the proximity of the redox-switching moiety to the catalytically active site (vide infra), another important factor is the identity of the metal center used for catalysis. For example, while the yttrium complex is active for lactide polymerization in its reduced state, the indium complex that contains the same ancillary ligand is active for lactide polymerization in its oxidized state. Another factor is the identity of the reactant; different reactants can display orthogonal reactivity with respect to the oxidation state of the catalyst. For example, the iron complex (FIG. ) demonstrates redox switching for lactide and epoxide polymerization, but the active oxidation state for lactide and epoxide polymerization are the reduced and oxidized forms, respectively. While more examples are needed to understand these and other effects that have been observed, two related factors appear to be important in polymerization catalysis: the propensity for the reactant to bind to the catalytically active site and the electrophilicity/nucleophilicity of reactive intermediates. Both factors are altered by changing the oxidation state of the catalysts, and the relative importance of each is related to the nature of each reaction, including the identity of the metal centers and the monomers employed.