Abstract: The PHENIX experiment continues to study the spin structure of the nucleon at RHIC (Relativistic Heavy Ion Collider), the world's only polarized pp collider. A high luminosity run with longitudinally polarized collisions at a center of mass energy of 510 GeV in 2013 has enabled the study of the contribution of the gluon polarization to the overall spin of the proton in a kinematic region where no current experimental results exist to guide the theoretical understanding of spin decomposition for composite particles in QCD. This talk will focus on a recent analysis of the spin dependence of J/\psi production as well as other probes that will provide definitive progress towards the resolution of the so called "proton spin puzzle" that has persisted since the EMC (European Muon Collaboration) experiment in 1987.