The integration by parts formula on the Wiener space is transferred to
the Poisson space, where it is considered as a consequence of an isom
etry formula, Some applications are then dealt with: changes of measur
e obtained by adding or substracting masses to the Poisson measure; st
udy of a notion of Gibbs measure, and relation with the reversible mea
sures for the evolution of an interacting particle system; more genera
lly, study of the invariant measures for this system.