Motivated by the Super-Kamiokande atmospheric neutrino data, we discuss pos
sible textures for Majorana and Dirac neutrino masses within the see-saw fr
amework. There are two main purposes of this paper: first, to gain intuitio
n into this area from a purely phenomenological analysis, and second, to ex
plore to what extent it may be realized in a specific model. We comment ini
tially on the simplified two-generation case, emphasizing that large mixing
is not incompatible with a large hierarchy of mass eigenvalues. We also em
phasize that renormalization-group effects may amplify neutrino mixing, and
we present semi-analytic expressions for estimating this amplification. Se
veral examples are then given of three-family neutrino mass textures, which
may also accommodate the persistent solar neutrino deficit, with different
assumptions for the neutrino Dirac mass matrices. We comment on a few feat
ures of neutrino mass textures arising in models with a U(1) flavour symmet
ry. Finally, we discuss the possible pattern of neutrino masses in a "reali
stic" flipped SU(5) model derived from string theory, illustrating how a de
sirable pattern of mixing may emerge. Both small- or large-angle MSW soluti
ons are possible, while a hierarchy of neutrino masses appears more natural
than near-degeneracy. This model contains some unanticipated features that
may be relevant in other models also: The neutrino Dirac matrices may not
be related closely to the quark mass matrices, and the heavy Majorana state
s may include extra gauge-singlet fields.