The purpose of the Phd is to analyze questions raised by short-termism in takevoer bids. As a matter of fact, some shareholders only have short-terme strategies (such as Hedge funds,...) and takeover bids provide some fantastic arbitration opportunities. First, one should clearly identify these actors. Products which might be used in such situation will also have to be studied. Second, one should analyze which defence could provide the target. Third, a study of the opportunity or repealing or amending french legislation on these issues will be done.