COMPASS and HERMES contributions to our understanding of the nucleon spin

An update is given on the ongoing experimental investigation of the spin structure of the nucleon, with particular emphasis on the results from the COMPASS and HERMES experiments. Both longitudinal and transverse spin phenomena are covered. In the first case, the hot topic is the direct measurement of the gluon polarization. Evidence is presented for Δ G / G being small around x g ≃ 0.1 , and the first moment of Δ G should not be larger than 0.2–0.3. About transverse spin effects, evidence is given for new phenomena, associated with transverse-momentum-dependent distribution and fragmentation functions, which might explain the transverse spin phenomena observed for a long time in pp scattering.