This chapter focuses on the impact of CEE countries on the development of climate and energy policies at the EU level. It is argued that states in the region demonstrate some shared preferences and utilise regional groupings to promote these at the EU level. The chapter discusses the contribution of CEE countries to the development of EU policy – such as Polish efforts to create an ‘Energy NATO’, CEE countries’ efforts to improve energy security following the 2006 and 2009 gas crises, the 2014 Energy Union, and the reaction to the full-scale Russian invasion of Ukraine in 2022. The chapter argues that the security dimension was given priority by CEE countries at the EU level. They contributed to placing energy security on the EU’s agenda during accession negotiations and the immediate post-accession period; however, their preferences were often not shared by older members. It was the 2006 and 2009 gas supply disruptions that shifted the focus towards energy security in the region, and at the EU level. In 2022 the EU’s dependency on and vulnerability to high levels of energy imports from Russia were brought into sharp focus.