Since the observation of the EMC experiment that only a small fraction of the nucleon spin can be attributed to the quarks spins and that the strange quark sea seems to be negatively polarised the internal spin structure of the nucleon has been further investigated in detail by several polarised deep-inelastic lepton-nucleon scattering experiments.

The results of these experiments and our present understanding of the polarised quark and gluon distributions will be reviewed with special emphasis on the HERMES experiment at HERA/DESY.

The perspectives for the next round of experiments, which will start data taking in 2001 (COMPASS@CERN, HERMES@HERA, STAR and PHENIX@RHIC), will be summarised.