In contrast to existing economic theory on the choice of legal standards in the enforcement of Competition Law, we develop a modelling framework that accounts explicitly for (a) Courts' choices, given the substantive standard adopted and (b) Competition Authorities (CAs) setting legal standards anticipating Courts' choices, recognizing that CAs place at least some weight on the implications of their choices for the outcome of the judicial review process and, hence, for their reputation. We then show why CAs may favor Per Se type standards (even when an error-minimising or welfare maximization approach would suggest the choice of an effects-based standard), with sub-optimal utilization of economic analysis, how this choice is affected by the Courts' substantive standards, why the legal standards for any given conduct may differ between countries, why there may be a U-shaped empirical relationship between legal standards and the probability that the CA's decisions are annuled and how the choice of standards affects other aspects of enforcement, such as the number of investigations undertaken. [ABSTRACT FROM AUTHOR]