ATLAS measurements of minimum bias and soft QCD

The first measurements of charged particle production in proton-proton collisions at center-of-mass energy sqrt(s)=900 GeV and 7 TeV recorded with the ATLAS detector at the LHC are presented. Minimum bias distributions are measured for events with at least one charged particle in the kinematic range |eta|<2.5 and p_T > 500 MeV and compared with the predictions from various Monte Carlo models. Activity in the underlying event was measured with respect to the highest p_{T} track in the event. A new PYTHIA6 Monte Carlo tune, ATLAS Minimum Bias Tune 1, was produced using ATLAS minimum bias distributions measured in a diffractive limited phase-space in combination with measurements from previous hadron collider experiments. The new tune is shown to significantly improve the predictions for minimum bias distributions measured in the diffractive limited phase-space.