The concept of ancillary restraint refers to any restraint directly related and necessary to the implementation of a main transaction that is itself in compliance with the competition rules. The importation into French law of the theory of ancillary restraints, which constitutes a variant of the rule of reason, is recent. If the main transaction covered by the agreement does not restrict competition, it is not necessary to examine the compatibility of the individual restrictions contained in the agreement. As in European law, the restriction must be objectively necessary to the main transaction, which has not been found to be the case with respect to multilateral commissions fixed by mutual agreement between competing banks for each check remittance. Moreover, the Competition Authority considers that restraints that have been notified and authorized in the context of a merger operation cannot, by virtue of the acquired rights doctrine, be examined ex post facto with regard to the rules on anticompetitive practices.