Cyclic polymers do not contain end groups, and as a result they demonstrate a number of unique physical properties. For example, the density, refractive index, Tg, viscoelasticity, reptation, and surface properties of cyclic polymers all differ from those of their more common linear analogs. Over the past fifty years a handful of catalysts have been discovered that can create cyclic polymers. In this seminar, four new catalysts will be presented that are capable of creating cyclic polymers. Aspects of catalyst design and two distinct mechanisms of polymerization will be discussed. A common theme in this research is the use of strained, tri- and tetra-anionic pincer ligands. Metal-ligand features that accentuate reactivity will be discussed, including the concept of an “Inorganic Enamine”. Dynamic and static light scattering techniques provide <Rg2> and RH ratios of cyclic vs. linear samples that clearly indicate a difference in topology. Complementing the light scattering data, intrinsic viscosities ([η]) measured over a wide-range of molecular weights clearly demonstrate the topological relationship between authentic linear and cyclic samples.