LIOUVILLE AND JACOBI THEOREMS FOR VECTOR DISTRIBUTIONS Olga Krupkov\'{a} Abstract. The paper contains a generalization of the Liouville and Jacobi integration methods, known from the classical calculus of variations, to the case of characteristic distributions of closed $2$-forms of constant rank on smooth manifolds. It is shown that the results can be used to find integral manifolds of completely integrable distributions on smooth manifolds. In this way, the theorems of Liouville and Jacobi are generalized to a wide class of generally higher order ordinary and partial differential equations, possibly degenerate, which are not supposed to come from a Lagrangian. Keywords: completely integrable distribution, closed $2$-form, characteristic distribution of a closed $2$-form, Liouville theorem, Jacobi theorem, symmetries of differential equations, integration of differential equations, degenerate equations, non-variational equations, connections on fibered manifolds. MS classification: 58A30, 34A05, 34A08, 70H10, 70H20.