Who could have predicted that the S´ eminaire de Probabilit´ es would reach the age of 40? This long life is first due to the vitality of the French probabil- tic school, for which the S´ eminaire remains one of the most specific media of exchange. Another factor is the amount of enthusiasm, energy and time invested year after year by the R´ edacteurs: Michel Ledoux dedicated himself tothistaskuptoVolumeXXXVIII,and Marc Yormadeh is name inseparable from the S´ eminaire by devoting himself to it during a quarter of a century. Browsing among the past volumes can only give a faint glimpse of how much is owed to them; keeping up with the standard they have set is a challenge to the new R´ edaction. In a changing world where the status of paper and ink is questioned and where, alas, pressure for publishing is increasing, in particular among young mathematicians, we shall try and keep the same direction. Although most contributions are anonymously refereed, the S´ eminaire is not a mathema- cal journal; our first criterion is not mathematical depth, but usefulness to the French and international probabilistic community. We do not insist that everything published in these volumes should have reached its—nal form or be original, and acceptance–rejection may not be decided on purely scientific grounds.