X-ray Polarimetry is expected to be a powerful tool to study astrophysical sources deriving data on their geometry and on the emission mechanisms. It can also provide a tool to answer to questions of fundamental physics. While X-ray polarimetry has been soon recognized as a powerful tool  from the dawn of the X-ray Astronomy era,  the only positive result so far is the measurement of the polarization of the Crab Nebula that dates back in the seventies. However a number of missions were proposed since then either based on the classical techniques of Bragg diffraction and Thomson/Compton scattering and on  the modern techniques such as photoelectric effect in gas. These attempts  were complemented by theoretical works providing updated expectations. In this talk I will review the main motivations for making today sensitive X-ray polarimetry experiments describing the most promising techniques and possible mission profiles for future measurement.