The Emissions Trading System (ETS) of the (EU) is the largest carbon trading market in the world, but climate change is a global challenge. In 2009, the EU announced its ambition of having linked carbon markets OECD-wide by 2015. This article assesses the EU’s progress in reaching this goal, inquires whether the explanatory factors lie within the EU itself or in the external environment, and discusses the main prospects for the future. Despite some progress, no interconnected emission trading system will cover the entire OECD area by 2015—so the EU is lagging behind in terms of achieving its own ambitions. Within the EU, member-state pressure for external linking has been modest, with Germany and the UK as notable exceptions. The European Commission has worked to establish links between the EU ETS and other systems, with only modest backing from other EU bodies. Globally, the development of emissions trading has progressed slowly. Furthermore, external interest in linking up with an increasingly crisis-ridden EU ETS has been variable, with, for instance, reluctant US actors and an eager Australian government. Experience thus far indicates that the bottom–up route to a global climate regime offered by linking is a long-term project—certainly not a “quick fix.