In commutative algebra, André–Quillen cohomology is a theory of cohomology for commutative rings which is closely related to the cotangent complex. The first three cohomology groups were introduced by Stephen Lichtenbaum and Michael Schlessinger and are sometimes called Lichtenbaum–Schlessinger functors T0, T1, T2, and the higher groups were defined independently by Michel André and Daniel Quillen using methods of homotopy theory. It comes with a parallel homology theory called André–Quillen homology.