  We review detector technologies which are currently considered for ultimate
nucleon decay searches, new generation astrophysical neutrinos studies, and for
future long-baseline neutrino experiments at new high-intensity neutrino beam
facilities. We focus our discussion on Phase-II experiments with a timescale of
$10\simeq 20$ years. We point out that there are very few detector technologies
which are general purpose and versatile enough in order to potentially address
non-accelerator based physics and a large variety of future neutrino beam types
ranging from superbeams, betabeams and neutrino factories from subGeV to 10's
GeV energies.
