The ATLAS pixel detector

A silicon pixel detector has been chosen for the innermost region of the ATLAS experiment. In addition to being a new technology sitting in a particularly hostile environment, the ATLAS experiment imposes some difficult constraints of its own on this detector. This demands an ambitious development program. The first generation of front-end chips have recently been bonded to detectors and tested in a beam of 180 GeV pions. Presented here is a description of the demands on the ATLAS pixel system and the first encouraging results.