  Since evidence for neutrino oscillations was first observed in 1998, the
study of muon neutrino oscillations has been aggressively pursued. In doing so,
atmospheric and accelerator-based neutrino experiments have measured with the
highest precision two fundamental neutrino parameters: the mass-square
difference and the large mixing angle in the atmospheric neutrino sector.
Furthermore, the dominant mode of these oscillations has recently been
established to be from muon to tau neutrinos with both direct and indirect
observations. Also, for the first time the anti-neutrino counterparts to these
oscillation parameters are being studied. While a consistent picture of the
mu-tau sector is thus emerging, a new generation of accelerator-based
experiments using off-axis neutrino beams to access this sector could lead to
new discoveries.
