Extremely high energy cosmic rays and the Auger Observatory

Over the last 30 years or so, a handful of events observed in ground-based cosmic ray detectors seem to have opened a new window in the field of high-energy astrophysics. These events have energies exceeding 5/spl times/10/sup 19/ eV (the region of the so-called Greisen-Zatsepin-Kuzmin spectral cutoff); they seem to come from no known astrophysical source; their chemical composition is mostly unknown; no conventional accelerating mechanism is considered as being able to explain their production and propagation to Earth. Only a dedicated detector can bring in the high-quality and statistically significant data needed to solve this long-lasting puzzle: this is the aim of the Anger Observatory project around which a world-wide collaboration is being mobilised. A large amount of information and technical documents can be consulted on many Web pages accessible through: http://www-lpnhep.in2p3.fr/auger/.