Narrow-band X-ray polarizing filters.

We review past and current attempts to measure X-ray polarization in celestial sources and describe research activity into a new family of materials which have been shown to exhibit linear dichroism at X-ray wavelengths. Such materials could add a polarimetry capability to the high energy resolution detectors proposed for future, high effective area, X-ray astrophysical observatories such as Constellation-X and XEUS. They have the potential to achieve useful minimum detectable polarization values for a number of sources in a sensible exposure time with XEUS.