Abstract. Jacobi/Poisson algebras are algebraic counterparts of Jacobi/Poisson manifolds. We introduce representations of a Jacobi algebra A and Frobenius Jacobi algebras as symmetric objects in the category. A characterization theorem for Frobenius Jacobi algebras is given in terms of integrals on Jacobi algebras. For a vector space V a non-abelian cohomological type object J H 2 (V, A) is constructed: it classifies all Jacobi algebras containing A as a subalgebra of codimension equal to dim(V ). Representations of A are used in order to give the decomposition of J H 2 (V, A) as a coproduct over all Jacobi A-module structures on V . The bicrossed product P ⊲⊳ Q of two Poisson algebras recently introduced by Ni and Bai appears as a special case of our construction. A new type of deformations of a given Poisson algebra Q is introduced and a cohomological type object HA 2 P, Q | (⊳, ⊲, ↼, ⇀) is explicitly constructed as a classifying set for the bicrossed descent problem for extensions of Poisson algebras. Several examples and applications are provided.