Marie-Thérèse Levasseur ([tɛ.ʁɛz lə.va.sœʁ]; 21 September 1721 – 12 July 1801; also known as Thérèse Le Vasseur, Lavasseur) was the domestic partner, mistress, wife and widow of Genevan philosopher Jean-Jacques Rousseau.

Thérèse Le Vasseur came from a respected family that had fallen on hard times; her father had a small official position relating to currency in Orléans, which he lost by 1744, and her mother was a shop-keeper; this business having failed,[1][2] Thérèse and her mother moved to Paris to find work, and were later joined by her father.

Le Vasseur was working as a laundress and chambermaid at the Hotel Saint-Quentin in the rue des Cordiers, where Rousseau took his meals.

Therese provided Rousseau with support and care, and when he died, she was the sole inheritor of his belongings, including manuscripts and royalties.

After Rousseau's death in 1778, she married Jean-Henri Bally, a valet of René de Girardin, in November 1779.