Neutrino mass limit from tritium β decay

This paper reviews recent experiments on tritium β-spectroscopy searching for the absolute value of the electron neutrino mass m(ν_e). By the use of dedicated electrostatic filters with high acceptance and resolution, the uncertainty on the observable m²(ν_e) has been pushed down to about 3 eV². The new upper limit of the mass is m(ν_e) < 2 eV at 95% C.L. In view of erroneous and unphysical mass results obtained by some earlier experiments in β decay, particular attention is paid to systematic effects. The mass limit is discussed in the context of current neutrino research in particle- and astrophysics. A preview is given of the next generation of β-spectroscopy experiments currently under development and construction; they aim at lowering the m²(ν_e) uncertainty by another factor of 100, reaching a sensitivity limit m(ν_e) < 0.2 eV.