This chapter examines the specific features that made US antitrust and EU competition law particularly conducive to a republican understanding of economic liberty and translated the structural goal of preserving a polycentric market structure into concrete competition policy. It sheds light on how the ideal of republican liberty and the idea of a competition–democracy nexus were given shape through a specific legal modus operandi, such as the structure of legal commands, standards of assessments, and institutional principles. The chapter identifies the (i) extensive use of broadly construed rule-like presumptions of anticompetitiveness, a (ii) possibilist standard of harm, and (iii) a precautionary error–cost framework erring in the case of doubt on the side of over-deterrence (type I errors) as the main channels of republican antitrust in the US and EU. These legal filters can be considered the main parameters or policy levers of a distinctive republican approach towards antitrust law and policy.