ALT Relying solely on mild ultraviolet or visible light irradiation of thiocarbonylthio compounds, we have developed a new avenue to polymer-protein conjugates, semi-telechelic polymers, and well defined ultrahigh molecular weight block polymers. Using either a photocatalyst or relying on the direct activation of photoactive functional groups, we are able to (i) synthesize polymers by photoiniferter polymerization and (ii) install new functionality to these polymers to prepare copolymers of (meth)acrylates and olefins that are inaccessible by direct copolymerization. Extending these approaches to the rapidly growing field of photocatalytic decarboxylation, we were also able to prepare photodegradable polymers that have all-carbon backbones. Most recently, we have demonstrated that by employing the traditional conditions of photopolymerization at elevated temperatures, we are able to achieve dramatically accelerated depolymerization to regenerate monomer.