  A simultaneous understanding of the results of the LSND experiment indicating
$\nu_{\mu}-\nu_e$ oscillation together with other evidences for neutrino
oscillations from solar and atmospheric neutrino data seems to require the
existence of at least one sterile neutrino. One can also give other plausible
astrophysical arguments that seem to require light sterile neutrinos. A major
theoretical challenge posed by their existence is to understand why they are so
light. A scenario is presented where one assumes a parity doubling of the
standard model with identical matter and gauge content. The neutrinos of the
parity doubled (mirror) sector are light for the same reason that the known
neutrinos are light and since they do not couple to the known W and Z bosons,
they can be identified with the sterile neutrinos. Some of the implications and
possible tests of this hypothesis are mentioned.
