This study investigates the law in books and law in action of antitrust enforcement in Germany, the EEC, and the USA. Using the classic methodological principle of comparison, functionality, it analyzes the interdependence - the conflicts and the cooperation - between private and public enforcement. For instance, a legal order might not give a victim standing to sue for damages while another one does; perhaps, however, the victim has an adequate right to make the cartel agency act to its benefit, a right it might lack in the other legal order. The analysis is followed by some reform suggestions. - Conducting this investigation, the author focuses on an important and too little explored question in comparative law: the ways in which differing legal systems with roughly similar substantive law enforce that law.