Although it has fallen from the political agenda to some extent in the years since the 2009 UN climate change conference in Copenhagen, climate change remains a serious threat to long-term prosperity in Europe, Asia, and globally. While one of the drivers of European activism on climate change has undoubtedly been a concern with addressing the risks posed by unmitigated climate change, the issue has also been used instrumentally by European policy entrepreneurs to advance the process of EU integration. This paper traces this process of climate policy institution-building within the EU over the period from 1990 onwards, in particular comparing the 1990s, the 2000s, and the post-2010 period. During the 1990s, institution-building was relatively unsuccessful. However, the 2000s saw the creation of much deeper integration, characterized by EU-level institutions and policies to tackle climate change. The period since 2010, however, has seen a partial waning of enthusiasm for climate activism in the EU, though existing institutions and policies remain in place. The paper identifies factors which explain variation in the success of institution-building efforts over the period since 1990. It draws particular attention to the relative importance of the internal and external drivers of integration, arguing that external factors have provided a crucial context which facilitated European integration in this policy field. The conclusion draws on the European experience in responding to climate change through regional integration in order to reflect on processes of regionalism in Asia, and argues that EU-style integration in this area is unlikely to be repeated in the Asian continent.