GIULIANO MUSSATI Why do mergers occur, which are their effects on social welfare and which is the best economic policy toward them? These three questions have been puzzling industrial economists since the end of the last century when the first great merger wave has come about in the US. They have returned at the centre of the stage of the theoretical and empirical economic research during the last decade when merger and acquisition activity became one of the most evident firms' activities in all industrialised countries, being fostered by some general and country specific facts. These facts...