  We begin with a brief overview of highest-energy cosmic ray data, and the
experiments which will perform neutrino astronomy. We then discuss two particle
physics aspects of neutrinos. They are possible long-lifetime decay of the
neutrino, and a measurement of the neutrino-nucleon cross-section at a CMS
energy orders of magnitude beyond what can be achieved with terrestrial
accelerators. Measurement of an anomalously large neutrino cross-section would
indicate new physics (e.g. low string-scale, extra dimensions, precocious
unification), while a smaller than expected cross-section would reveal an
aspect of QCD evolution. We then discuss aspects of neutrino-primary models for
the extreme-energy (EE) cosmic ray data. Primary neutrinos in extant data are
motivated by the directional clustering at EE reported by the AGASA experiment.
We discuss the impact of the strongly-interacting neutrino hypothesis on
lower-energy physics via dispersion relations, the statistical significance of
AGASA directional clustering, and the possible relevance of the Z-burst
mechanism for existing EE cosmic ray data.
