  We review the problem of neutrino masses and mixings in the context of Grand
Unified Theories. After a brief summary of the present experimental status of
neutrino physics, we describe how the see-saw mechanism can automatically
account for the large atmospheric mixing angle. We provide two specific
examples where this possibility is realized by means of a flavour symmetry. We
then review in some detail the various severe problems which plague minimal GUT
models (like the doublet-triplet splitting and proton-decay) and which force to
investigate the possibility of constructing more elaborate but realistic
models. We then show an example of a quasi-realistic SUSY SU(5) model which, by
exploiting the crucial presence of an abelian flavour symmetry, does not
require any fine-tuning and predicts a satisfactory phenomenology with respect
to coupling unification, fermion masses and mixings and bounds from proton
decay.
