The parameters characterising neutrino masses, mixing and phases are subject to a worldwide experimental and theoretical research activity. We briefly review the status of such parameters in the standard three-neutrino framework, and discuss related open issues. We then consider an extension of the standard framework including heavy neutrinos in addition to the light ones, and discuss the implications for the determination of the effective Majorana mass parameter through neutrinoless double beta decay, in the hypothesis of negligible interference of light and heavy contributions. Far-future prospects in this field are mentioned.