The spin structure of the nucleon: A phenomenological introduction

The investigation of the spin structure of the nucleon via semi-inclusive deep inelastic scattering on polarized nucleons is updated with the most recent results of the JLab, HERMES, and COMPASS experiments. A short description is given of these experiments, which are complementary in phase space and use sophisticated and different techniques to polarize the nucleon targets. The cases of target spin parallel or orthogonal to the direction of the incoming lepton require different experimental techniques, have a different phenomenology and need a different theoretical treatment. After reviewing these differences, the most recent transverse spin advances are presented, and evidence is given that the new data already allow for a rather precise extraction of the transversity and of the Sivers PDFs.