Gribov-Regge theory, partons, remnants, strings – and the EPOS model for hadronic interactions

We discuss the key ingredients of realistic hadronic interaction models for air shower developments, like parton evolutions, high parton density effects, remnants, multiple scattering, and string fragmentation. We will focus in particular on the EPOS approach, which has been extensively tested against RHIC, SPS, and TEVATRON data. We will also discuss recent developments concerning collective effects like the hydrodynamic evolution of a quark gluon plasma in hadronic interactions.