  Recent neutrino mass experiments at Mainz and Troitsk using tritium
beta-decay have reached their sensitivity potential, yielding upper limits of
about 2 eV/c^2 for the electron antineutrino mass. The KArlsruhe TRItium
Neutrino experiment (KATRIN), designed to reach a sensitivity of 0.2 eV/c^2
(90% C.L.), will improve the signal rate by a factor of about 100 with respect
to previous experiments while maintaining the same low background level at an
enhanced energy resolution of 0.93 eV of the spectrometer which is scaled up by
a factor of 10 in linear dimensions. This low background rate can only be
achieved by active and passive reduction of the background components induced
by the spectrometer itself and in the detector region. Furthermore, sources of
systematic errors such as energy losses inside the tritium source or
fluctuations of the energy scale of the spectrometer need to be carefully
controlled and analysed. An overview of KATRIN's method to reduce the
background rate and to determine the systematics as well as the sensitivity on
the neutrino mass will be presented.
