HERMES measurements of spin asymmetries

The double spin asymmetries in semi-inclusive deep inelastic scattering and in the quasi-real photoproduction of high pT hadron pairs have been measured at the HERMES experiment. While the former asymmetries allow a determination of the polarised quark distributions of different flavour, the latter one is interpreted as first direct experimental evidence for a positive gluon polarisation. Finally, a measurement of an azimuthal single-spin asymmetry in semi-inclusive pion production is presented and interpreted as an effect of a new T-odd fragmentation function