This volume features papers presented at the Hadronic Shower Simulation Workshop. The workshop brought together world experts in the field to establish a collaborative effort that would lead to a better understanding and simulation of hadronic showers relevant to hadron calorimetry at the ILC and LHC, neutrino fluxes and atmospheric showers. The workshop evaluated existing event generator and transport codes. Before the workshop a benchmark analysis was carried out, whereby various hadronic shower simulation scenarios were submitted to code developers and the results were presented at the workshop. The workshop identified the shortcomings of existing hadronic shower simulations and brought out the need to acquire new data to improve shower models.