Probing few-nucleon systems using spin

Understanding the few-nucleon system remains one of the challenges in modern nuclear and hadron physics. Observables in few-nucleon scattering processes are sensitive probes to study the two and many-body interactions between nucleons in nuclei. In the past decades, several facilities provided a large data base to study in detail the three-nucleon interactions below the pion-production threshold by exploiting polarized proton and deuteron beams and large-acceptance detectors. This paper gives a brief overview of the experimental results and their interpretation exploiting ab-initio calculations derived from the state-of-the-art nucleon-nucleon forces. In particular, the role of spin in the proton-deuteron break-up channel is being highlighted.