  Current generation neutrino telescopes cover an energy range from about 10
GeV to beyond $10^9$ GeV. IceCube sets the scale for future experiments to make
improvements. Strategies for future upgrades will be discussed in three energy
ranges. At the low-energy end, an infill detector to IceCube's DeepCore would
add sensitivity in the energy range from a few to a few tens of GeV with the
primary goal of measuring the neutrino mass hierarchy. In the central energy
range of classical optical neutrino telescopes, next generation detectors are
being pursued in the Mediterranean and at Lake Baikal. The KM3NeT detector in
its full scale would establish a substantial increase in sensitivity over
IceCube. At the highest energies, radio detectors in ice are among the most
promising and pursued technologies to increase exposure at $10^9$ GeV by more
than an order of magnitude compared to IceCube.

Instrumentation and Methods for Astrophysics