  The see-saw mechanism to generate small neutrino masses is reviewed. After
summarizing our current knowledge about the low energy neutrino mass matrix we
consider reconstructing the see-saw mechanism. Low energy neutrino physics is
not sufficient to reconstruct see-saw, a feature which we refer to as ``see-saw
degeneracy''. Indirect tests of see-saw are leptogenesis and lepton flavor
violation in supersymmetric scenarios, which together with neutrino mass and
mixing define the framework of see-saw phenomenology. Several examples are
given, both phenomenological and GUT-related. Variants of the see-saw mechanism
like the type II or triplet see-saw are also discussed. In particular, we
compare many general aspects regarding the dependence of LFV on low energy
neutrino parameters in the extreme cases of a dominating conventional see-saw
term or a dominating triplet term. For instance, the absence of mu -> e gamma
or tau -> e gamma in the pure triplet case means that CP is conserved in
neutrino oscillations. Scanning models, we also find that among the decays mu
-> e gamma, tau -> e gamma and tau -> mu gamma the latter one has the largest
branching ratio in (i) SO(10) type I see-saw models and in (ii) scenarios in
which the triplet term dominates in the neutrino mass matrix.
