  We summarize the measurements investigating the nucleon spin structure done
at Jefferson Lab, a multi-GeV continuous electron beam facility located in
Newport News, Virgina, USA. After motivating spin structure studies, we explain
how Jefferson Lab uniquely contributes to them and describe the experimental
program that was achieved with energies up to 6 GeV. We then discuss the
continuation of this program at the higher energies now available thanks to the
recent 12 GeV upgrade of Jefferson Lab's accelerator.
