Nucleon spin structure studies at Jefferson Lab

We report on the low and moderate Q^2 nucleon spin structure measurements done at Jefferson Lab, examining specifically the inclusive program. We discuss what the data teach us about quark confinement and the emergence of the effective hadronic degrees of freedom from the fundamental partonic ones. We show how this experimental program has reached its goal by providing a precise mapping at low, intermediate and moderately high Q^2 which has followed in many advances, e.g., with Chiral Perturbation Theory. Another example of a recent advance imputable to the JLab spin data is the improved understanding of \alpha_s at low energy, which allowed Light-Front Holographic QCD, an approximation to non-perturbative QCD, to derive the hadron spectrum from \Lambda_s.