  This is a review article about neutrino mass models, particularly see-saw
models involving three active neutrinos which are capable of describing both
the atmospheric neutrino oscillation data, and the large mixing angle MSW solar
solution, which is now uniquely specified by recent data. We briefly review the
current experimental status, show how to parametrise and construct the neutrino
mixing matrix, and present the leading order neutrino Majorana mass matrices.
We then introduce the see-saw mechanism, and discuss a natural application of
it to current data using the sequential dominance mechanism, which we compare
to an early proposal for obtaining large mixing angles. We show how both the
Standard Model and the Minimal Supersymmetric Standard Model may be extended to
incorporate the see-saw mechanism, and show how the latter case leads to the
expectation of lepton flavour violation. The see-saw mechanism motivates models
with additional symmetries such as unification and family symmetry models, and
we tabulate some possible models, before focussing on two particular examples
based on SO(10) grand unification and either U(1) or SU(3) family symmetry as
specific examples. The article contains extensive appendices which include
techniques for analytically diagonalising different types of mass matrices
involving two large mixing angles and one small mixing angle, to leading order
in the small mixing angle.
