  In this talk we assume the conventional see-saw mechanism, and contruct a
hierarchical pattern of three active neutrinos with bi-maximal mixing. In order
to enforce the hierarchy we use the single right handed neutrino dominance
mechanism which is a very nice way to ensure a neutrino mass hierarchy in the
presence of large mixing angles. We show how this mechanism can be organised in
the framework of a U(1) family symmetry, then discuss a realistic
string-inspired model which includes such a symmetry.
