The X-ray satellite SAX, a major program of the Italian Space Agency with participation of the Netherlands Agency for Aereospace Programs, was launched on April 30 1996 from Cape Canaveral. After launch it was renamed BeppoSAX in honour of Giuseppe (Beppo) Occhialini. The payload is characterized by a very wide spectral coverage from 0.1 to 300 keV, with well balanced performances both from its low and high energy instrumentation. Its sensitivity will allow the exploitation of the full band for weak sources (1/20 of 3C 273), opening new perspectives in the study of spectral shape and variability of several classes of objects. Furthermore, the presence of wide field cameras will allow monitoring of the long term variability of sources down to 1 mCrab and the discovery of X-ray transient phenomena. In this paper we describe the main aspects of the mission, the operations, the scientific capabilities of the instruments and the scientific objectives.