ABSTRACT
This chapter analyses the horizontal mergers in the United States and the European Union. A presentation of American and European merger enforcement and of the political and economic backgrounds of the efficiency defence will introduce a discussion of its treatment in both jurisdictions. Antitrust was a concern for the American legislatures, with the enactment of the Clayton Act in 1914 to complement the Sherman Act of 1890. The acceptance of efficiency arguments to authorise a merger harming competition departs from an otherwise competition-driven analysis centred on market shares and numerical data. It is only that efficiency considerations have begun to play a significant role in merger analysis, especially in the United States. While the efficiency defence is increasingly prevalent and explicitly acknowledged in the assessment of mergers by the US courts and agencies, the European Commission has been reluctant and even hostile to such claims.
