  The initial demonstrations over the last several years of the use of optical
diffraction radiation (ODR) as non-intercepting electron-beam-parameter
monitors are reviewed. Developments in both far-field imaging and near-field
imaging are addressed for ODR generated by a metal plane with a slit aperture,
a single metal plane, and two-plane interferences. Polarization effects and
sensitivities to beam size, divergence, and position will be discussed as well
as a proposed path towards monitoring 10-micron beam sizes at 25 GeV.
