Introduction; 1. The research question and scope of the study; 2. Practical relevance of the research question; 3. Methodology and structure; Part I. Comparison of Antitrust and International Trade Law: 4. Emphasizing differences or commonalities?; 5. Antitrust law; 6. WTO/GATT law; 7. Congruence in efficiency and welfare standards; Part II. The Role of Market Definition: 8. Antitrust law; 9. Article III of the GATT; 10. Conclusion; Part III. Analytical Evolution from the Traditional to the Economic Approach: 11. The traditional formalistic approach; 12. The economic approach; 13. Assessment of the analytical evolution; 14. Conclusion; Part IV. Conceptualizing an Economic Approach to Market Definition: 15. Introduction; 16. Market definition framework: a matter of treaty interpretation; 17. The content of a marketplace-test; 18. Potential competition; 19. The relevant 'market' concept; 20. The role of the traditional criteria; 21. Making sense of the different Article III prohibitions; 22. Conclusion; Part V. The Implementation of an Economic Approach: Quantitative Methods: 23. Introduction; 24. The law and economics of expert economic testimony; 25. Analysis of price elasticities of demand.