  Starting from 1960s, a great number of missions and experiments have been
performed for the study of the high--energy sky. This review gives a wide
vision of the most important space missions and balloon experiments that have
operated in the 10--600 keV band, a crucial window for the study of the most
energetic and violent phenomena in the Universe. Thus it is important to take
the stock of the achievements to better establish what we have still to do with
future missions in order to progress in this field, to establish which are the
technologies required to solve the still open issues and to extend our
knowledge of the Universe.
