"Hadrons, the building blocks of all matter in Nature, are not fundamental but composed of quarks and gluons. Up to now we do not know HOW NATURE MAKES HADRONS one of the most important questions of contemporary structure-of-matter physics. Major breakthroughs are to be expected with new experimental facilities such as FAIR. Most studies in hadron physics at HESR/FAIR will employ beams of unpolarized antiprotons, but the most spectacular opportunities will arise for polarized antiprotons the physics case is exceptional. The flag-ship experiment, Drell-Yan production in double polarized proton-antiproton scattering, gives direct access to transversity , the terra incognita of nucleon spin structure. The provision of such beams presents enormous scientific / technological challenges and has never been achieved with intensities sufficient for the crucial experiments. State-of-the-art techniques are capable of producing intensities less than ~10^5 s-1, which cannot be efficiently accumulated. It is the aim of this project to develop an efficient method for POLARIZING ANTIPROTON BEAMS by in-situ build-up in a storage ring. The only viable method to do this effectively is through "spin-filtering" by the repeated interaction of an antiproton beam with a polarized hydrogen gas target in a cooler storage ring. This technique works with protons, but it is not clear how the polarization build-up happens in detail. Spin-filtering needs to be optimized and, in particular, it must be extended to antiprotons. Within the framework of this project, the aim is to provide polarized antiproton beams in a storage ring with at least WITH 10 ORDERS OF MAGNITUDE higher intensity than previously possible. A very experienced team of scientists and engineers is needed, and this is available within my group. We will also strongly benefit from our collaboration partners. Thus, it is a "now or never" opportunity. If successful, a new era will open with fascinating experiments."