In the first piece of the external commentary series, J.A. Lewis, Director of the Strategic Technologies Program at the Center for Strategic and International Studies, discusses the importance of stronger measures for the European Union to have a well-rounded active cyber defence. This commentary, originally delivered as a transatlantic keynote during the eurepoc conference, highlights the significance of attribution, proportional responses, and international cooperation. These aspects of active cyber defence can deter adversaries and build accountability in cyberspace, which is especially relevant in light of rising tensions and the increased frequency and severity of offensive attacks on democratic states.