  Soft QCD contributes to all observables at the LHC, due to the presences of
underlying event (UE) and pile-up in all events. Both these processes are
dominated by multi-parton interactions (MPI), i.e. the result of proton
collisions containing more than one partonic interaction due to collective and
beam remnant effects. While there is undoubtedly interesting physics involved
in MPI, the primary interest of LHC experiments is to characterise and model
the behaviour of UE and pile-up sufficiently well that their influence may be
cleanly subtracted in the process of searching for new physics signatures at 7
TeV and beyond. I summarise the soft QCD measurements made by ATLAS using the
2010 and early 2011 datasets, and the use of this data to improve Monte Carlo
generator models of MPI for use in forthcoming simulation campaigns.
