Since the 1992 Maastricht Treaty, which brought into being the Common Foreign and Security Policy, the path of European integration has meant the difference between a strong and secure Europe and the disintegration of a grand, idealistic experiment. In this post-9/11 world, with recent terrorist attacks in Madrid and London, and several attempted terrorist plots foiled, Europe now faces a critical juncture when it comes to dealing with the problem of security. Sovereignty is the key obstacle to security integration because security has traditionally been the prerogative of individual member-states. Are strongly held beliefs about sovereignty ceding ground to an untested supranational order? I argue that key epistemic communities of military strategists, technology experts, and diplomats are already breaking down this resistance because they are in a unique position to persuade others of certain shared norms.These knowledge-based networks, or "epistemic communities", are comprised of non-governmental professionals who share policy relevant expertise, and have actually gained acceptance for the beginnings of a European homeland security. I seek to explain why they are succeeding in pushing forward security integration despite the strong inclination for national governments to hold onto this authority. In this paper, I compare three epistemic communities - military strategists, technology experts, and diplomats - to shed light on the interaction of competing epistemic communities with different motivations and norms. A shortcoming of the current epistemic community literature is that it tends to assume that each epistemic community is operating in a transnational vacuum. Even though I demonstrate that all three epistemic communities support further security integration, their motivations, preferences, processes of socialization, and shared norms vary immensely.I engage in process-tracing and comparative case-studies for each of these epistemic communities to determine the origins of their allegiance, the social background of their membership, the creation and evolution of norms, their overlap with other epistemic communities, and the subsequent success or failure of their efforts to persuade and socialize others. In particular, I seek to determine the degree of impact these norms have had on the general political will for security integration. In this regard, I focus primarily on elite-level acceptance, and whether this has led to particular policy outcomes that support the gradual development of a kind of homeland security in Europe. The implications for sovereignty, democracy, and the limits of integration cannot be ignored. ..PAT.-Unpublished Manuscript [ABSTRACT FROM AUTHOR]