The ATLAS (A Toroidal LHC ApparatuS) detector for the Large Hadron Collider at CERN, which is under construction, will study the products of proton‐proton collisions at energies of up to 14 TeV. The outermost part of the ATLAS detector, the Muon Spectrometer, is designed to identify muons with high efficiency, and measure their momenta with a resolution of ∼10&percent; at pT=1 TeV/c. The measurement is performed inside the toroidal field created by powerful air‐core toroid magnets with the help of the ATLAS Muon precision tracking system. Three Greek universities have taken the responsibility to construct 30,000 drift tubes of ∼1.7 m length, to test them and finally assemble them into 120 BIS (Barrel Inner Small) chambers. The design of the muon drift tubes aims at high detection efficiency (>95&percent;) and a spatial single tube resolution of <80 &mgr;m. © 2003 American Institute of Physics