  Neutrino beams at from high-energy proton accelerators have been instrumental
discovery tools in particle physics. Neutrino beams are derived from the decays
of charged pi and K mesons, which in turn are created from proton beams
striking thick nuclear targets. The precise selection and manipulation of the
pi/K beam control the energy spectrum and type of neutrino beam. This article
describes the physics of particle production in a target and manipulation of
the particles to derive a neutrino beam, as well as numerous innovations
achieved at past experimental facilities.
