  The atmospheric neutrino anomaly is the apparent reduction of the
$\nu_{\mu}/\nu_{e}$ ratio observed in underground detectors. It represents
either a reduction in the muon neutrino interaction rate or an excess of the
electron neutrino interaction rate, or both.
  Unable to answer the question of ``What else could it be?'' this paper
explores a number of alternatives which do not seem to be viable. Various
methods to reduce the apparent muon rate or to increase the apparent electron
rate are discussed.
  Perhaps our bias that the interactions are due to neutrinos of atmospheric
origin is incorrect. Both of these assumptions need to be confirmed. Efforts to
reduce uncertainties in the estimated atmospheric neutrino flux would also help
to narrow the possibilities further.
