Let B be a commutative Bézout domain B and let M Spec(B) be the maximal spectrum of B. We obtain a Feferman-Vaught type theorem for the class M od B of B-modules. We analyse the definable sets in terms, on one hand, of the definable sets in the classes M od BM , where B M ranges over the localizations of B at M ∈ M Spec(B), and on the other hand, of the constructible subsets of M Spec(B). When B has good factorization, it allows us to derive decidability results for the class M od B , in particular when B is the ring Z of algebraic integers or the one of rings Z ∩ R, Z ∩ Q p .MSC 2010 classification: 03C60, 03B25, 13A18, 06F15.