Russia’s invasion of Ukraine has driven the European Union and the United Kingdom to decouple from Russian oil and gas. What does decoupling mean, and how will it affect Europe’s security? In the short run can the European Union and the United Kingdom secure the natural gas and energy flows it needs to sustain public support? Over the coming decade, the European Union and the United Kingdom have committed to energy systems that are resilient and environmentally sustainable. Can they attract investment to succeed and compete? How will these transitions affect the Trans-Atlantic relationship? Europe’s future in NATO? Europe’s own security institutions?