European defence cooperation is expanding rapidly in response to geopolitical instability, from Russia’s invasion of Ukraine to growing uncertainty about the long-term reliability of transatlantic security guarantees. New financing instruments, industrial policies, and coordination mechanisms are accelerating the development of a more integrated European defence architecture. Yet institutional reforms and funding alone cannot sustain this transformation. Defence remains one of the most politically sensitive domains of governance in Europe, touching directly on sovereignty, public spending, and national identity. As cooperation deepens, its viability will increasingly depend on how these policies are communicated to and understood by European citizens. In a fragmented information environment marked by disinformation and strategic competition, public opinion itself becomes a critical arena of security governance. Building European defence therefore requires not only stronger institutions and industrial capacity, but also clearer public communication capable of sustaining democratic legitimacy.