The effectiveness and credibility of enforcement requires that there is access to ex post review of competition cases by an independent court or tribunal. Judges assess both procedural due process as well as compliance with the substantive provisions of competition law and can confirm enforcement decisions, or identify mistakes and seek to correct them. Some jurisdictions allow a full merits review of competition decisions without limitation of the legal grounds while others on limited grounds. Understanding the standard of review of competition enforcement that courts follow is therefore important. This paper was prepared as a background note for a discussion held at the OECD in June 2019 on the standard of review by courts in competition cases.