This article documents the evolution of “cap and trade” as a policy response to global climate change. Through an analysis of 33 distinct policy venues, the article describes how the cap and trade policy domain has developed along spatial, temporal, and institutional dimensions. This discussion demonstrates that following initial discussions of cap and trade in the Kyoto Protocol negotiations, the idea quickly spread to other policy venues, creating a complex system of multilevel governance, where many questions about how to govern emissions trading remain contested. The analysis contextualizes recent questioning of emissions trading as an appropriate mechanism for controlling GHG emissions, as well as the ongoing debates about who should govern cap and trade and how it should be carried out. The findings highlight the value added of a domain-level perspective and suggest the need for future research on the sociopolitical nature of cap and trade policy debates.