The COMPASS Experiment at CERN has a broad physics program aimed at the study of nucleon spin structure and hadron spectroscopy. It has an outstanding fixed-target apparatus, mostly commissioned in 2001, presently consisting of a solid 6 LiD polarised target and a two stage spectrometer with high resolution tracking, particle identification and calorimetry, capable of standing high event rates. This paper describes the apparatus and its performances during the run of 2002, when 260 TB of

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... ed muon nucleon scattering data have been collected. First physics signals from the analysis and projections for the expected accuracy of the measurement of the gluon polarisation AG/G from photon gluon fusion are presented too.