  Neutrino factories, neutrino beams produced in the decay of a muon or
antimuon beam inside a storage ring, yield cleaner, richer, and more flexible
neutrino beams relative to super-beams. We explore the physics case for this
type of beam both for standard oscillation as well as new physics searches and
present some machine options. We argue that there is a rich program beyond what
the current neutrino program can cover and a string synergy with the muon
collider program.
