  Physics potential of future measurements of atmospheric neutrinos is
explored. Observation of $\Delta m^2_{21}$ driven sub-dominant effects and
$\theta_{13}$ driven large matter effects in atmospheric neutrinos can be used
to study the deviation of $\theta_{23}$ from maximality and its octant.
Neutrino mass hierarchy can be determined extremely well due to the large
matter effects. New physics can be constrained both in standard atmospheric
neutrino experiments as well as in future neutrino telescopes.
