  I review progress toward the experimental study of polarized proton
collisions at RHIC, at center-of-mass energies of several hundred GeV. The
tools under development for these experiments are summarized, with emphasis on
the complementarity for the spin program of the two major detectors, PHENIX and
STAR. The proposed research program includes measurements of the spin structure
of hadrons, tests of QCD predictions for spin observables, and polarization
searches for interactions beyond the Standard Model. I argue, in particular,
that RHIC should provide the best determination of the gluonic contribution to
proton spin foreseen for the coming decade.
