Polarized Parton Distributions and QCD Spin Tests at RHIC-BNL

The RHIC facility at BNL will be operating soon, part of the year, as a polarized proton-proton collider. This will allow the undertaking of a vast spin physics programme, mainly by the two large detectors PHENIX and STAR. We review some theoretical aspects of this research programme which will allow, firstly to improve our present knowledge on polarized quark, gluon and sea distributions in a nucleon, secondly to perform novel QCD spin tests and finally, perhaps, to uncover some new physics.