  Cosmic high energy neutrinos are inextricably linked to the origin of cosmic
rays which is one of the major unresolved questions in astrophysics. In
particular, the highest energy cosmic rays observed possess macroscopic
energies and their origin is likely to be associated with the most energetic
processes in the Universe. Their existence triggered a flurry of theoretical
explanations ranging from conventional shock acceleration to particle physics
beyond the Standard Model and processes taking place at the earliest moments of
our Universe. Furthermore, many new experimental activities promise a
considerable increase of statistics at the highest energies and a combination
with gamma-ray and neutrino astrophysics will put strong constraints on these
theoretical models. The detection of ultra high energy neutrinos in particular
is made likely by new experimental techniques and will open an important new
channel. We give an overview over this quickly evolving field with special
emphasize on new experimental ideas and possibilities for probing new physics
beyond the electroweak scale.
