  This work discusses the perspectives to observe fluxes of high energy
astrophysical neutrinos with the planned km3 telescopes. On the basis of the
observations of GeV and TeV gamma-rays, and of ultra high energy cosmic rays,
it is possible to construct well motivated predictions that indicate that the
discovery of such fluxes is probable. However the range of these predictions is
broad, and the very important opening of the ``neutrino window'' on the high
energy universe is not guaranteed with the current design of the detectors. The
problem of enlarging the detector acceptance using the same (water/ice
Cherenkov) or alternative (acoustic/radio) techniques is therefore of central
importance.
