The observation of high energy neutrinos will open a new window on the universe. The primary aim of the experiment is to use neutrinos as a tool to study particle acceleration mechanisms in energetic astrophysical objects such as active galactic nuclei and gamma-ray bursts, which may also shed light on the origin of ultra-high-energy cosmic rays. At somewhat lower energies, non-baryonic dark matter (WIMPs) may be detected through the neutrinos produced when gravitationally captured WIMPs annihilate in the cores of the Earth and the Sun, and neutrino oscillations can be measured by studying distortions in the energy spectrum of upward-going atmospheric neutrinos.