The Sigma telescope - A decisive step in high energy astronomy

A review is presented of the Sigma telescope, the main element of the Soviet satellite Granat launched in 1989. The Granat's principal mission is the study of high energy astronomy, providing a unique opportunity to explore those regions where considerable energy transfers take place. Attention is given to the Galactic and extragalactic targets selected, the general orbit parameters, and the basic elements of the telescope.