In mathematics, given a G-torsor X → Y and a stack F, the descent along torsors says there is a canonical equivalence between F(Y), the category of Y-points and F(X)G, the category of G-equivariant X-points. It is a basic example of descent, since it says the "equivariant data" (which is an additional data) allows one to "descend" from X to Y. When G is the Galois group of a finite Galois extension L/K, for the G-torsor , this generalizes classical Galois descent (cf. field of definition).