  Ultrahigh energy neutrinos can provide important information about the
distant astronomical objects and the origin of the Universe. Precise knowledge
about their interactions and production rates is essential for estimating
background, expected fluxes and detection probabilities. In this paper we
review the applications of the high energy QCD to the calculations of the
interaction cross sections of the neutrinos. We also study the production of
the ultrahigh energy neutrinos in the atmosphere due to the charm and beauty
decays.
