  A pedagogical summary of current and past experimental results of
spin-dependent nucleon structure prior to the arrival of the Electron-Ion
Collider is attempted. After an introduction, results from fixed-target
experiments at SLAC, Fermilab, Jefferson Lab, CERN and DESY and collider
experiments from RHIC are presented, starting with the longitudinal spin
structure of the nucleon, followed by generalized parton distributions (GPDs),
which map the proton in transverse position space. The final part discusses
transverse proton or parton spin and transverse parton momenta (TMDs), and
their their (spin-orbit) correlations, which are addressed by a multitude of
recent experimental results. The GPDs and TMDs provide complementary pathways
to mapping multi-dimensional nucleon structure.
