The study of ultra-high energy cosmic rays provides information about the hadronic interactions in an energy and kinematic region well beyond those explored in accelerators. The Pierre Auger Observatory is the largest cosmic ray observatory ever built (3000 km$^2$ ), operating since 2004
in the Argentinian Pampa. Its hybrid design allows one to measure the longitudinal and lateral distribution of extensive air showers and the establishment of an almost model-independent, calorimetric, energy scale. The observatory is sensitive to the electromagnetic and to the muonic components of extensive air showers, which are directly related to the energy and type of the primary particle and to the hadronic interaction parameters. In this contribution an overview of the results obtained by the Auger collaboration in the field of particle physics will be given. We will show the proton-Air cross section at 38.7 and 55.5 TeV. Our data indicate that hadronic
interaction models fail in the predictions of the muon densities on the surface, too low with respect
to the measured ones. Possible future lines of research to investigate this inconsistency will be
identified.