  The HERMES experiment has measured double spin asymmetries of inclusive and
semi-inclusive cross sections for the production of charged hadrons in
deep-inelastic scattering of polarised positrons on polarised hydrogen and
deuterium targets, in the kinematic range 0.023 < x < 0.6, and 1 GeV^2 < Q^2 <
15 GeV^2. For the data taken on the deuterium target, a RICH detector provides
the complete identification of charged pions and kaons. From the inclusive
measurements on deuterium, the polarised structure function g_1^d has been
extracted with high precision. Together with the semi-inclusive measurements,
quark polarisations are extracted separately for the u, ubar, d, dbar, and (s +
sbar) flavours in a LO QCD analysis. Furthermore, a possible breaking of
flavour symmetry in the polarised light sea, (Delta ubar - Delta dbar), was
measured for the first time and found to be consistent with zero within the
experimental precision.
