Dr. Fred Sarazin Colorado School of Mines The cosmic ray spectrum spans many orders of magnitude in energy. At the very end of the spectrum (E>10^18 eV) lie the Ultra High Energy cosmic rays (UHECRs). Their origin remains largely unknown and their study is made difficult in part by the very low flux impinging on Earth's atmosphere. The Pierre Auger Observatory, located in the Mendoza province of Argentina, is an array of detectors spread over 3000 km^2 specifically designed to study the properties of the extensive air showers induced by the UHECRs in the atmosphere. The Observatory is fully operational since 2008 and is operated by a collaboration of more than 500 scientists and engineers from 19 countries. In this colloquium, a selection of recent results obtained by the Observatory and the plan for the upcoming upgrade will be presented.