Neutrino-less Double Beta Decay and beyond the Standard Model Physics

A brief sketch is given of the present observational status and future prospects of the physics of neutrino mass, including a survey of the various theoretical schemes of neutrino mass generation. Emphasis is given to those which are motivated by present experimental hints from solar and atmospheric neutrinos, as well as from cosmological data related to the dark matter question. The conceptual importance of neutrino-less double beta decay as a distinctive signature of the Majorana character of neutrinos is stressed. Barring accidental cancellations this process gives the strongest laboratory constraint on neutrino mass.