This project studies the formation of expectations of antitrust commissions and courts with regard to market developments in the event of corporate mergers in the USA and Germany between 1945 –1989. The merger control established by legislation in the USA and Germany in the 20th century was not only subject to the specific expectations of legislators but also obliged antitrust commissions and courts in both countries to form economic expectations in different legal systems. How do legislators, antitrust commissions, and courts form expectations about the relationship between enterprise size and competition? On which ideas about competition is this formation of expectations based, how is it adopted, modified, rejected? How do the formations of legislative, commission, and court expectations interact? The project should also be able to give an answer to the question, if and to what extent the competition policy regimes of both regulation areas are characterized by convergence.