  Present limits on neutrino masses are briefly reviewed, along with
cosmological and astrophysical hints from dark matter, solar and atmospheric
neutrino observations that suggest neutrino masses. These would imply many
possible new phenomena such as neutrinoless $\beta\beta$ decay, lepton flavour
violating processes such as neutrino oscillations, $\mu \ra e \gamma$, $\mu \ra
3 e $, $\mu \ra e$ conversion in nuclei, as well as two-body decays with the
emission of a superweakly interacting spin zero particle, called majoron, e.g.
$\mu \ra e + J$. All of these processes may occur at levels consistent with
present or planned experimental sensitivities. The underlying physics may also
be probed at the high energies accessible at LEP, through related Z decay
processes. Another possible, albeit quite indirect, manifestation of massive
neutrinos is in Higgs physics. As an example I discuss the possibility of an
invisibly decaying Higgs, a quite generic feature of majoron models where the
lepton number is spontaneously violated close to the electroweak scale.
