  Soon after the discovery of the first extrasolar X-Ray sources it was
suggested that polarimetry could play a major role as a diagnostic tool.
Attempts to measure polarization of X-Ray sources was performed by the team of
Columbia University lead by Robert Novick. The technique of Bragg diffraction
at 45{\deg} was successful to detect the polarization of the Crab with rockets
and with OSO-8 satellite. In the following evolution of X-Ray Astronomy,
Polarimetry was too mismatched with the improved sensitivity of imaging and
spectroscopy, based on the use of optics. As a consequence no polarimeter was
flown any more. At the beginning of the century a new class of instruments
based on the photoelectric effect were developed. In the focus of an X-Ray
telescope they can perform angular, energy and time resolved polarimetry and
benefit of the large increase of sensitivity due to the optics. The Imaging
X-Ray Polarimetry Explorer, exploiting this technique, was launched at the end
of 2021.
