ABSTRACT:
The origin of Ultra High Energy Cosmic rays (with energy larger than 10^{18} [eV]) still remain a mystery. The spectrum, arrival directions and composition (type of nuclei, associated photon/neutrino fluxes) are the key players in the task of disentangling this puzzle. Different approaches and experimental techniques are being pursued to derive these quantities. In this talk I will review the recent results from The Pierre Auger Observatory, one of the leading experiments in the field. I will also present the fundamentals of a new analysis technique developed by the author and a small group of collaborators aiming to increase the available statistics for composition studies. Finally, I will discuss the role of hadronic interactions in our understanding of Cosmic Ray data and the role of LHC data (pushing from the low energy side) in decreasing systematic uncertainties.