<p>Polymers and plastics pose environmental challenges, including marine pollution from waste and CO₂ emissions from incineration. Recycling and upcycling are crucial strategies for conserving petroleum resources and reducing waste discharge. Additionally, developing sustainable polymers is essential for achieving a circular economy. Polymer degradation is a key process in both recycling and sustainable polymer development. This review examines the degradation of condensation polymers, such as polyesters and polycarbonates, when organic catalysts are used to enhance transesterification. Organic bases exhibit high catalytic efficiency in polymer degradation, whereas others facilitate the controlled polymerization of substituted cyclic esters and carbonates. Notably, 1,5,7-triazabicyclo[4.4.0]dec-7-ene has exceptional efficiency in degrading various condensation polymers, including aliphatic polycarbonates and liquid-crystalline wholly aromatic polyesters, via a dual hydrogen-bonding activation mechanism. The functionalization of aliphatic polycarbonates via side-chain modifications is a promising approach for producing functionalized degradable polymers, supported by efficient monomer synthesis and established ring-opening polymerization (ROP) techniques using organic catalysts. Precise polymer synthesis enhances mechanical and thermal properties by incorporating rigid moieties while enabling degradation control. These advancements contribute to the development of sustainable materials within a future circular economy.</p>