[en] COMPASS is a new fixed target experiment at CERN to study the nucleon spin structure with a polarized muon beam and a polarized nucleon target. Gluon spin contribution to the nucleon spin will be studied by measuring the asymmetry of open charm production or high P_T hadron pair production in semi-inclusive deep inelastic scattering of a polarized muons on a polarized nucleon target. The COMPASS spectrometer is a two-stage spectrometer equipped with ring image Cherenkov counters and calorimeters. The run will start to take data in 2001. (author)