  The two calorimeters CASTOR and ZDCs enhance the hermeticity of the CMS
detector at the LHC by extending the rapidity coverage in the forward region.
After having described these detectors, their forward physics capabilities are
presented. These latters include the study of parton shower, multiple parton
interactions, diffraction and ultra high energy cosmic rays models. The
processes to be measured to constrain these topics are multi-jet events with a
forward jet, central-forward activity correlation, rapidity gaps and forward
neutron production.
