The Pierre Auger Observatory is the largest detector for cosmic rays with energies above EeV. The Observatory has established a clear suppression of the fluxes of the highest energy particles, charged nuclei, which are expected to come from extragalactic sources. The contribution of photons and neutrinos from more exotic sources is strongly limited. Cosmic rays are detected through the extensive air showers produced by collisions at centre-of-mass energies that extend above those tested at the LHC. Detailed analyses of the showers are key to identify the primary particle types and also to test the modelling of high energy hadronic interactions. Indeed, the available models do not perfectly describe the collected data, and currently the Auger surface detectors are being upgraded to provide more direct information on the shower particles. This talk will focus on the shower physics analyses and their impact on cosmic ray and hadronic interaction studies.