  The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the mass
of electron neutrinos from beta-decay of tritium with an unprecedented
sensitivity of 0.2 eV/c^2 improving present limits by one order of magnitude.
The decay electrons will originate from a 10 m long windowless, gaseous tritium
source. Super-conducting magnets guide the electrons through differential and
cryogenic pumping sections to the electro-static tandem spectrometer
(MAC-E-filter), where the kinetic energy will be measured. The experiment is
presently being built at the Forschungszentrum Karlsruhe by an international
collaboration of more than 120 scientists. The largest component, the 1240 m^3
main spectrometer, was delivered end of 2006 and first commissioning tests have
been performed. This presentation describes the goals and technological
challenges of the experiment and reports on the progress in commissioning first
major components. The start of first measurements is expected in 2012.
