Based on the study of the professional careers of 439 parliamentary assistants of the 7th parliamentary term (2009–2014), we identify their different career patterns, especially after leaving the European parliament. We show which factors (social, biographical) influence mobility within the field of Eurocracy. We assess the importance of public/private circulation. Beyond the notorious ‘revolving doors’ and the question of the transfer of information from EU institutions to private interests, we show that parliamentary assistants form a group of specialised intermediaries of EU affairs who, after having acquired specific knowledge and know-how at the heart of European policymaking, are able to convert these assets in different sectors (public bureaucracies, private companies, or NGOs), at the EU level or in the member states. Such mobility illustrates the blurring of the public/private divide, and the hybridisation of EU governance. We thus shed new light on the structuring of the field of Eurocracy and the circulation of professionals within it.