We propose a generic method for obtaining quickly good upper bounds on the minimal value of a multistage stochastic program. The method is based on the simulation of a feasible decision policy, synthesized by a strategy relying on any scenario tree approximation from stochastic programming and on supervised learning techniques from machine learning. 1 Context Let Ω denote a measurable space equipped with a sigma algebra B of subsets of Ω, defined as follows. For t = 0, 1,. .. , T − 1, we let ξ t be a random variable valued in a subset of an Euclidian space Ξ t , and let B t denote the sigma algebra generated by the collection of random variables ξ [0: t−1] def = {ξ 0 ,. .. , ξ t−1 }, with B 0 = {∅, Ω} corresponding to the trivial sigma algebra. Then we set B T −1 = B. Note that B 0 ⊂ B 1 ⊂ • • • ⊂ B T −1 form a filtration; without loss of generality, we can assume that the inclusions are proper-that is, ξ t cannot be reduced to a function of ξ [0: t−1]. Let π t : Ξ → U t denote a B t-measurable mapping from the product space Ξ = Ξ 0 × • • • × Ξ T −1 to an Euclidian space U t , and let Π t denote the class of such mappings. Of course Π 0 is a class of real-valued constant functions. We equip the measurable space (Ω, B) with the probability measure P and consider the following optimization program, which is a multistage stochastic program put in abstract form: S : min π∈Π E {f (ξ, π(ξ))} subject to π t (ξ) ∈ U t (ξ) almost surely. (1) Here ξ denotes the random vector [ξ 0. .. ξ T −1 ] valued in Ξ, and π is the mapping from Ξ to the product space U = U 0 × • • • × U T −1 defined by π(ξ) = [π 0 (ξ). .. π T −1 (ξ)] with π t ∈ Π t. We call such π an implementable policy and let Π denote the class of implementable policies. The function f : Ξ × U → R ∪ {±∞} is B-measurable and such that f (•, ξ) is convex for each ξ. It can be interpreted as a multi-period cost function. The sets U t (ξ) are defined as B t-measurable closed convex subsets of U t. A set U t (ξ) may implicitly depend on π 0 (ξ),. .. , π t−1 (ξ) viewed as B t-measurable