Exploring the Universe with Ultra High Energy Cosmic Rays

Ultra High Energy Cosmic Rays (UHECR) are messengers of the most powerful astrophysical sources in the universe and they offer the unique chance of investigating particle interactions over an energy range well beyond the one covered by present ground-based particle accelerators. Despite several progresses have been made in the last decade, the understanding of the nature of UHECR and of their origin remains an open science case. A review of selected results from the largest UHECR experiments, namely The Pierre Auger Observatory and the Telescope Array, is presented with the emphasis given to the measurements of energy spectrum, arrival directions, chemical composition, and the search for photons and neutrinos as primary particles. Connection to hadronic physics and open issues will also be discussed along with the perspectives for near future measurements