Claudine Alexandrine Guérin de Tencin, Baroness of Saint-Martin-de-Ré (27 April 1682 – 4 December 1749) was a French salonist and author. She was the mother of Jean le Rond d'Alembert, philosophe and contributor to the Encyclopédie, though she left him on the steps of the Saint-Jean-le-Rond de Paris church a few days after his birth.