A myriad of new techniques and technologies made it possible to inaugurate the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory as the world's first high-energy polarized proton collider in December 2001. RHIC delivers polarized proton-proton collisions at center-of-mass energies of up to 500 GeV. This unique environment provides opportunities to study the polarized quark and gluon spin-structure of the proton and QCD dynamics at a high energy scale and is therefore complementary to existing semi-inclusive deep inelastic scattering experiments. This talk summarizes recent achievements of the RHIC spin program and their impact on our understanding of the nucleon’s spin structure, i.e. the individual parton (quarks and gluons) contributions to the helicity structure of the nucleon and to understand the origin of the transverse spin phenomena.