This book examines the struggle of the European Union bureaucracy to maintain its autonomy in an increasingly complex institutional setting and adverse political environment. Using an original survey of nearly two hundred top European Commission officials, it shows that the Commission is a coherent organization that shares a common culture of supranationalism. The European Union's multicephalous structure of political authority limits the capacity of European politicians to curb the autonomy of the Commission but tends to undermine the legitimacy of the organization, which finds itself under persistent political attacks. These attacks inadvertently help the organization bolster its defenses against the external threats and trigger internal legitimation processes that reinforce the devotion of its employees to its institutional mission. The rich survey data show how Commission bureaucrats establish themselves as the 'custodians of Europe'. The book helps disentangle the complexity of the Commission and makes a contribution to the study of international bureaucracies, a topic that has received little attention.