Nucleons are bound-states of quarks and gluons (partons), which interact through the strong force described by Quantum Chromodynamics (QCD). Even if, together with electrons, they are the most important building blocks of ordinary matter, we still poorly know how their properties (like spin) are generated by the dynamics of their constituent partons. Only now we are starting to unravel their complex structure in modern experiments (like CERN, DESY, RHIC or JLAB, among others), which is a great challenge, since we cannot isolate them. In this talk I will give an overall review of the theoretical and phenomenological status of the field, and what can we learn about QCD by probing nucleon 3-dimensional and spin structure.