2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/180368Various ways of determining the absolute neutrino masses are briefly reviewed and their sensitivities compared. The apparent tension between the announced but unconfirmed observation of the $0νββ$ decay and the neutrino mass upper limit based on observational cosmology is used as an example of what could happen eventually. The possibility of a ``nonstandard'' mechanism of the $0νββ$ decay is stressed and the ways of deciding which of the possible mechanisms is actually operational are described. The importance of the $0νββ$ nuclear matrix elements is discussed and their uncertainty estimated.Invited talk at the NOW2006 Workshop, Otranto, Italy, September 2006High Energy Physics - Phenomenologytext