  In view of the observation by IceCube of high-energy astrophysical neutrinos,
it is important to quantify the uncertainty in the background of atmospheric
neutrinos. There are two sources of uncertainty, the imperfect knowledge of the
spectrum and composition of the primary cosmic rays that produce the neutrinos
and the limited understanding of hadron production, including charm, at high
energy. This paper is an overview of both aspects.
