This chapter starts with exploring why jurisdictions chose trading – instead of carbon taxes. It examines the main similarities and differences across systems and their design properties. The design properties are: Type of system, Ambition level, Allowance allocation, Coverage, Offsets and linking, Monitoring, reporting and verification (MRV) and enforcement, Price/quantity management and Revenue earmarking. For each focused design feature, the chapter discusses the extent to which and how policy diffusion can explain the similarities and differences observed. It also discusses some concluding reflections on the challenges and opportunities for future research on the politics of emissions trading and the prospects ahead for carbon markets and their role in the implementation of the Paris Agreement. In China, as well, an important contributing factor in the choice of emission trading was ineffective command-and-control efforts to improve energy intensity. In South Korea, rapid economic growth and related greenhouse gas (GHG) emissions were not matched by effective climate policies.