Studying the role of lawyers specialising in competition law, this paper shows that they are essential intermediaries between the European administrative field and the private sector. Using both qualitative (interviews and archives) and quantitative (database) methods, it demonstrates that intermediation activities developed in the late 1980s with the arrival of American law firms, which exported their working methods to Europe. This led to a fierce competition between law firms, which tried to recruit from inside the European Commission. Circulation between the European institutions started to be common and slowly became regulated, a process that gave it legitimacy. While new activities developed for a part of the legal profession, most notably lobbying and intermediation activities, lawyers contributed to blurring the border between the public and the private sphere at the European level. The importance of circulation between the administrative sphere and law firms and the embeddedness between the public and the private sector are thus incentives for overcoming institutional frontiers when studying the European field of power. Because circulation facilitates the development of social networks, common practices, and shared representations, it is essential to maintaining coherence within this ‘weak field’.