The fight against climate change has become a major area of action for the European Union (EU), both at the European and the international level. EU climate policy has gained importance since the 1990s and is today the most politicized issue on the EU’s environmental agenda. The EU is often considered a frontrunner—even a leader—in the adoption of climate policies internally and the promotion of such policies externally. Internally, the EU has developed the world’s most advanced and comprehensive regulatory frameworks, encompassing both EU-wide policies and targets to be achieved by the member states. The actual EU policy instruments fall into two categories: whereas emissions in certain industrial sectors are reduced through a carbon market and a “cap-and-trade” system (the Emissions Trading Scheme), emissions from non-ETS sectors are addressed through domestic policies by member states. These measures have led to a reduction of greenhouse gas emissions in the EU, but they will not suffice to achieve the EU’s long-term goals, which requires a major overhaul of some of the basic premises of the EU’s policies in sectors such as energy production and consumption, transport, agriculture, and industry. Externally, the EU has been advocating ambitious and legally binding international climate agreements. Desiring to “lead by example”, the EU has been an influential global climate player at important international climate conferences such as those held in Kyoto (1997), Marrakesh (2001), and Paris (2015), but its diplomacy failed at the Copenhagen conference (2009).