To address the root of the plastics problem, the design of next-generation polymers must consider not only performance properties but also end-of-life options to establish closed-loop lifecycles towards a circular materials economy. In addition, synthetic and catalytic methodologies must be developed to enable expedient and selective depolymerization of end-of-life polymers for clean monomer recovery and polymer reproduction. Accordingly, this presentation will first introduce fundamental principles for designing circular polymers with not only intrinsic chemical recyclability but also tunable properties. Next, the development of catalytic routes will be described for the synthesis of designer monomers, circular polymers, and biodegradable plastics. Overall, the design and realization of such circular polymers must address three challenges: minimizing energy input, maximizing depolymerization selectivity, and overcoming depolymerizability/performance tradeoffs.