GPDs and underlying spin structure of the nucleon

It is shown that, based only upon two empirically known facts besides two reasonable theoretical postulates, we are inevitably led to a model-independent conclusion that the quark orbital angular momentum carries nearly half of the total nucleon spin at the low energy scale of nonperturbative QCD. Also shown are explicit model predictions for the forward limit of the unpolarized spin-flip GPDs, which are believed to give valuable information on the distributions of quark angular momentum inside the nucleon.