  Astrophysical false positives that mimic planetary transit are one of the
main limitation to exoplanet transit surveys. In this proceeding, we review the
issue of the false positive in transit survey and the possible complementary
observations to constrain their presence. We also review the false-positive
rate of both Kepler and CoRoT missions and present the basics of the
planet-validation technique. Finally, we discuss the interest of observing
bright stars, as PLATO 2.0 and TESS will do, in the context of the false
positives. According to simulations with the Besan\c{c}on galactic model, we
find that PLATO 2.0 is expected to have less background false positives than
Kepler, and thus an even lower false-positive rate.
