  We review the basic principles of X-ray polarimetry and current detector
technologies based on the photoelectric effect, Bragg reflection, and Compton
scattering. Recent technological advances in high-spatial-resolution gas-filled
X-ray detectors have enabled efficient polarimeters exploiting the
photoelectric effect that hold great scientific promise for X-ray polarimetry
in the 2-10 keV band. Advances in the fabrication of multilayer optics have
made feasible the construction of broad-band soft X-ray polarimeters based on
Bragg reflection. Developments in scintillator and solid-state hard X-ray
detectors facilitate construction of both modular, large area Compton
scattering polarimeters and compact devices suitable for use with focusing
X-ray telescopes.
