Private regulation has become a highly debated phenomenon. Previous research has focused mostly on the effectiveness, legitimacy, and governance structure of private regulators at the global level. Few existing analyses have focused on private regulation at the European level, where only questions of interest representation have attracted attention. Analyses of the contribution of private regulation to the process of European legal integration, in particular, are lacking. We seek to fill this gap. From private rules for product safety and for financial markets, such as the Single Euro Payments Area standards, to private rules governing the professions, we observe that private regulation has facilitated and accelerated European legal integration. We argue that in some cases this effect was anticipated, especially by the European Commission, and in those cases the intended effect on European legal integration at least partly explains the rise of private regulation. I other cases, it was an incidental by-product of attempts to address market failures or achieve network legitimacy. In the conclusion, we turn to questions of accountability and legitimacy raised by the increasing importance of private regulators in the Common Market of the EU. Although the EU lacks a body of rules that imposes democratic controls on private regulators, we identify components of European law that can be used as control mechanisms.