The chapter scrutinises the formation of a new type of legal expertise at the crossing between public and private law in France. It provides a sociological mapping of the blurring of ‘private-public’ divide through the rise of Parisian law firms and their historical repositioning in the French field of power as key brokers and a central crossroad in-between State and market actors. Through an in-depth analysis of more than two hundred individual career paths of leading politicians and high civil servants that have circulated from the various branches of the public sector (government offices, parliamentary committees, regulatory agencies, courts, etc.) to large corporate law firms (the so-called pantouflage), it offers a sociological assessment of the unprecedented blurring of the ‘public-private’ divide that has been taking place over the past two decades.