Since the 1980's development in polarized electron sources and polarized target techniques has brought the experimental study of the nucleon into a new era: The spin structure of the nucleon has been explored with polarized electron scattering. Now twenty years have passed. What have we
learned from the data? Do they agree with predictions from quantum chromo-dynamics (QCD), the theory for strong interactions? And what about
predictions from constituent quark models?
I will start from an introduction to the study of hadron structure using lepton deep inelastic scattering and give an overview of world data and
what we have already learned about nucleon structure. Then I will present results from a precision experiment completed at Jefferson Lab on the neutron spin in the valence quark region, and discuss about the future of this measurement.
The last 10 minutes of the talk will be devoted to a different topic: using polarized electron scattering to test the electro-weak Standard
Model and hadronic structure, and introducing the PV-DIS program that is being just launched at Jefferson Lab.
The talk will be given on an non-expert level.