This paper looks at the way policy entrepreneurs construct horizontal coherence through problem definition and the promotion of policy frames that bond different objectives and instruments together. Building on the case of the 2009 climate and energy package, the paper analyses how the European Commission and successive European Union Presidencies exploited a growing climate change momentum to devise, assemble and facilitate the adoption in an exceptionally short period of an ambitious legislative package cutting across traditional sectoral boundaries. The recourse to a narrative presenting Europe at the vanguard of a green revolution and the framing of European internal policies as a tool for international climate leadership were instrumental in constructing the package as a coherent response to the joint energy and climate change challenges, and in rallying wide support. However, the paper shows that the institutionalization of this framing has been undermined by the economic crisis and stalled international negotiations.