The Pierre Auger Observatory, now under construction in Argentina, will be an important tool in the solution of the puzzle of the ultra high energy cosmic rays. It will cover a total area of 6000 km2with 3200 surface Cherenkov detectors and 8 fluorescence detectors. The Pierre Auger Observatory is the result of an international effort. It has been designed to study cosmic rays with energies ⩾ 1018eV with high statistics, achieving its full efficiency at energies ⩾ 1019.5eV. The operation of a prototype detector in Argentina, deployed during the first stage of the construction in the southern site, has demonstrated the capability of the Pierre Auger Observatory to accomplish the objectives for which it was designed. The goal, the design and the status of the Pierre Auger observatory are briefly described in this paper. © 2003 American Institute of Physics