Search for Neutrinoless Double-Beta Decay

After the pioneering work of the Heidelberg-Moscow (HDM) and International Germanium Experiment (IGEX) groups, the second round of neutrinoless double-$\beta$ decay searches currently underway has or will improve the life-time limits of double-$\beta$ decay candidates by a factor of two to three, reaching in the near future the $T_{1/2} = 3 \times 10^{25}$ yr level. This talk will focus on the large-scale experiments GERDA, EXO-200, and KamLAND-Zen, which have reported already lower half-life time limits in excess of $10^{25}$ yr. Special emphasis is given to KamLAND-Zen, which is expected to approach the inverted hierarchy regime before future 1-ton experiments probe completely this life-time or effective neutrino-mass regime, which starts at $\approx 2 \times 10^{26}$ yr or $\approx 50$ meV.