The COMPASS experiment at CERN

To investigate the gluon polarisation of the nucleon the COMPASS experiment is being set up at the CERN muon beam. Using polarised deep inelastic scat tering the experiment exploits open charm production and correlated high P- T hadron pairs to tag photon gluon fusion. The expected precision for the m easured asymmetries will allow a significant determination of the gluon pol arisation for x(g) approximate to 0.1.