The S-S metathesis polymerization and depolymerization in Figure constitutes a new and efficient route to poly(trisulfide) polymers, complementing previously reported ring-opening polymerizations of cyclic trisulfides. More generally, this S-S metathesis polymerization provides access to sulfur-rich polymers, which have seen a resurgence due to the development of inverse vulcanization and related polymerizations by Pyun, and the many applications of these intriguing polymers. The reliable and high-yielding S-S metathesis polymerization and depolymerization is also a promising advance in developing analogs of commodity plastics that can be chemically recycled with high fidelity and efficiency. We have presented the poly(trisulfide) in Figure as a chemically recyclable analog of HDPE, but the concept could be applied in principle to many other polymer classes where the trisulfide serves as uniquely reactive end groups of monomers, oligomers, or preformed polymers. We envision using the metathesis of these trisulfide end groups as a platform technology that can be used to make and un-make a wide variety of useful macromolecules.