  Stored-muon-beam neutrino factories have been recognized as the best option
to measure precisely the elements of the MNSP matrix and sensitively test the
consistency of the three-neutrino mixing picture. Now that all three mixing
angles have been shown to be nonzero, the motivation for neutrino factory
construction is strong. A small number of feasibility issues remain open and
are the subject of ongoing R&D. Progress on these R&D efforts is described.
