The Pierre Auger Observatory is a large international effort to provide measurements of extensive air showers (EAS) initiated in the upper atmosphere by cosmic rays with energies above 10(18) eV , the Ultra High Energy Cosmic Rays (UHECR's). The explanations for the origin, acceleration processes and composition of the UHECR's face theoretical and experimental difficulties, due to the extremely low flux in this energy region. The full observatory will consist of a hybrid detector using an array of 1600 water <IMG SRC="/img/revistas/bjp/v34n4a/a16img01.gif">erenkov tanks spread over an area of 3000 km² overlooked by a set of 4 air fluorescence detectors per site. The southern site is being instrumented in Argentina and I will discuss its present status in this paper.
