The nuclear matrix elements will be combined with phase space factors to make predictions for half-lives and obtain limits on the average neutrino mass from current experiments. Other scenarios, in addition to the standard 3- neutrino scenario, will also be considered including the emission of a scalar particle, called the Majoron, in honor of Majorana, and the presence of sterile neutrinos, that is neutrinos with no standard model interactions, as suggested in 1957 by Pontecorvo.