and have led to a substantial modification of our understanding of Galactic structure and evolution. The importance of the ability of satellite observatories to survey and to study wavelengths which are inaccessible from the ground is evident in the wealth of data discussed and analysed in this volume which is derived from satellites, specifically COS-B, HEAD-I, HEAO-3, IRAS, PIONEER-lO, SAS-2, and TENMA. The cru­ cial role of ground-based observations to complement and comprehend the satellite data is also well evident. Similarly, the major ground-based studies whose results are reported here illustrate the necessity for carefully conceived and executed very large scale surveys of many types of object and many parts of parameter space before a coherent picture of the Galaxy will be available.