  The simultaneous beta decay of two neutrons in a nucleus without the emission
of neutrinos (called neutrinoless double beta decay) is a lepton number
violating process which is not allowed in the Standard Model of particle
physics. More than a dozen experiments using different candidate isotopes and a
variety of detection techniques are searching for this decay. Some (EXO-200,
Kamland-Zen, GERDA) started to take data recently. EXO and Kamland-Zen have
reported first limits of the half life $T_{1/2}^{0\nu}$ for $^{136}$Xe. After a
decade of little progress in this field, many new results will soon scrutinize
the claim from part of the Heidelberg-Moscow collaboration to have observed
this decay. The sensitivities of the different proposals are reviewed.
