Spin physics with COMPASS

COMPASS is a fixed target experiment at CERN studying nucleon spin structure in polarised deep inelastic muon nucleon scattering and hadron spectroscopy using hadron beams. The main goal of the COMPASS spin physics program is the measurement of the helicity contribution of the gluons to the nucleon spin, $\Delta G$. This quantity is accessible via the photon-gluon-fusion process which can be selected by open charm production or production of hadron pairs with large transverse momenta. The spin physics program of COMPASS includes also measurements with a transversely polarised target. These allow to measure the transverse structure function. COMPASS has up to now successfully finished three runs with a muon beam of 160 GeV and a longitudinally polarized $^{6}$LiD target in the years 2002, 2003 and 2004. An overview of the physics addressed by the muon program, with an emphasis on the $\Delta G/G$ measurement will be presented. The status of the analysis of the high $p_{T}$ hadron pairs, open charm, longitudinal and transverse asymmetries will be reviewed.