Longitudinal Spin Physics at RHIC and a Future eRHIC

Recent highlights from the spin program at the Relativistic Heavy Ion Collider (RHIC), focusing on the gluon contribution to the proton spin and the polarization of the light flavor sea, are presented. The impact of these data on recent global fits by the DSSV and NNPDF groups is also discussed. Finally, this note examines the constraints on the longitudinal spin structure of the proton which would be possible with a proposed eRHIC facility.