SOHO, the Solar and Heliospheric Observatory, is a project of international cooperation between ESA and NASA to study the Sun, from its deep core to the outer corona, and the solar wind. To achieve its scientific goals it carries a complement of twelve sophisticated, state-of-the-art instruments. Three helioseismology instruments are expected to provide unique data for the study of the structure and dynamics of the solar interior, from the very deep core to the outermost layers of the convection zone. A set of five complementary remote sensing instruments, consisting of EUV and UV imagers,...