High Energy Neutrino Cross Sections

The theoretical status of the neutrino-nucleon cross section is reviewed for incident neutrino energies up to Eν=1012 GeV, including different approaches to high energy extrapolations. Nonstandard model or nonperturbative physics may play a role at ultrahigh energies. The cases of mini-black hole production and electroweak instanton contributions are discussed as examples in the context of ultrahigh energy neutrino scattering.