  The physics case of the FP420 R&D project aiming at the installation of
proton detectors in the LHC tunnel at 420 m from the ATLAS and CMS interaction
points, is presented. The motivations of the measurements accessible with FP420
-- exclusive Higgs production (pp --> p H p) and photon-induced processes (pp
--> p gamma p --> p X p, pp --> p gamma gamma p --> p X p, where X is sensitive
to new physics) -- are outlined.
