  Polarized proton-proton collisions at the Relativistic Heavy Ion Collider
(RHIC) provide unique opportunities to study the spin structure of the nucleon.
We will highlight recent results on the nucleon spin structure from the STAR
and PHENIX experiments at RHIC: (1) A sizable gluon polarization in the proton
is measured with longitudinal double spin asymmetries of jet and hadron
production; (2) Longitudinal single spin asymmetries in W boson production
improve constraints on the sea quark polarization. The new spin asymmetry
results for W boson confirmed the SU(2) flavor asymmetry of the light sea quark
polarization in the proton; (3) Transverse spin effects in hadronic systems
offer new implications on parton distribution functions in the collinear and
transverse momentum dependent frameworks. We will also discuss near term plans
for the STAR forward detector upgrade and prospects for proton-proton and
proton-ion collisions in the years beyond 2021 at STAR.
