The cooperative interaction of four structurally different N-heterocyclic olefins (NHOs) with a range of simple metal halides as Lewis acidic cocatalysts is employed for the homo- and copolymerization of epsilon-caprolactone (CL) and delta-valerolactone (VL). While the single components are inactive on their own, their combination provides a powerful and operationally simple platform for the controlled preparation of polyesters from these monomers, whereby molecular weights and end groups can be predicted in a room temperature-based process using low catalyst loadings (0.25-0.50 mol %). A narrow molecular weight distribution is observed (1.05 < D-M < 1.15) for multiple combinations of NHOs and Lewis acids. Importantly, the supposed mechanism involves activation of the lactone monomers via coordination to the metal-based Lewis acids. This ensures rapid polymerization and additionally decouples reactivity and activity; a trade-off between fast monomer consumption and the suppression of side reactions (transesterification) can be circumvented this way. Furthermore, this dual catalytic setup can be used to direct preferential monomer incorporation when CL/VL are copolymerized. From the same 1:1 mixture of both monomers, either VL or CL can be consumed more rapidly, or more random incorporation can be achieved, depending on the employed cocatalysts. Well-defined copolymers with moderate gradients result, where the copolymerization selectivity is dictated by choice of the Lewis acid present, which is remarkable in view of the very different NHOs involved (saturated five- and six-membered rings, benzimidazole and imidazole derivatives). While most metal halides (such as MgI2, ZnI2, and AlCl3) entail VL-enriched polyester, YCl3 favors CL incorporation.