In the US, federal antitrust law may come into conflict both with federal regulation and regulatory schemes enacted by individual states. Similarly, in the EU, tensions can arise between EU antitrust rules, on the one hand, and either EU or member states' regulation, on the other. This paper seeks to examine the role played by legal tradition, in its manifold dimensions, in shaping the relationship between antitrust and regulation on the two sides of the Atlantic. To this end, Sections 2 and 3 will analyse the statutory provisions and doctrines governing the interplay between antitrust and regulation in the US and the EU. Sections 4 and 5 will explore each jurisdiction's legal traditions that may be relevant to the relationship between antitrust and regulation, such as the constitutional and political context of antitrust policy, the role of legal scholarship, and the antitrust enforcement culture. Section 6 will investigate possible connections between the divergences in the antitrust-regulation interface in the two legal systems and their different legal traditions.