  The nucleon is an ideal laboratory to solve QCD in the nonperturbative
regime. There are several experimental observations that still lack a rigorous
interpretation; they involve the nucleon as a (polarized) target as well as a
beam (in collisions and Drell-Yan processes). These data look like big
azimuthal and spin asymmetries, related to the transverse polarization and
momentum of the nucleon and/or the final detected particles. They suggest
internal reaction mechanisms that are suppressed in collinear perturbative QCD
but that are "natural" in Nuclear Physics: quark helicity flips, residual final
state interactions, etc.. In my talk, I will give a brief survey of the main
results and I will flash the most recent developments and measurements.
