EU climate policy has become gradually more ambitious in goals and policy instruments, strengthening the credibility of the EU’s leader-by-example ambition in the international climate negotiations. The chapter explores how the EU has been able to adopt an increasingly ambitious climate policy based on a modified supply–demand policy approach. Energy security concerns have provided a need for energy efficiency and more energy production. However, given differing interests among the member states and within the Commission, there is still a long way from energy needs to climate action. The institutional setting has provided an enabling context by stimulating consensus seeking and long-term policy development. A major obstacle throughout has been getting the new low-income member states to agree on a more ambitious climate policy. Explanations for change concern how policies and issues were combined in new ways that shared the costs, promoted new low-carbon opportunities and gave something to all the major ‘veto players’ involved in policy-making. The linkage between climate and energy policies has not come from societal demands, but broad support for EU-level climate policies has been important for legitimizing the decisions taken by EU leaders. The package of climate and energy policies was initiated despite low support for more ambitious EU-level renewable and energy efficiency policies, and in some member states there is only a weak link between public perceptions of climate action urgency and government positions.