A heavily cratered surface is a feature common to the early evolution of all the terrestrial planetary bodies. However, because the multiple impact history and inaccessibility of other bodies provide such poor geologic control, it is considered that the integrated effects of these impacts are best detailed and constrained through the intensive study of terrestrial impact structures. A survey of terrestrial structures indicates that the 65-km-diameter Manicouagan ring structure in Quebec, Canada, has by virtue of its size, exposure, and relatively well known geologic and geophysical characteristics the potential to provide details of impact processes, in particular those concerned with impact melting. This paper serves as an introduction to several detailed companion papers that resulted from a recent multidisciplinary study of Manicouagan. The major conclusions are as follows: The structure is 214 m.y. old. The melt rocks are texturally inhomogeneous but chemically homogeneous, can be modeled as a mixture of target lithologies, and have a 87Sr/86Sr ratio compatible with the melting of crustal rocks. Grain size and inclusion content of meld rocks vary inversely, grain size increasing upward. The melt had a two-stage cooling history with clast-melt interactions indicative of mixing superheated silicate liquid with cold clasts. Extensive digestion and reaction of clasts in the melt during the first stage of cooling resulted in a more refractory clast population than would be provided directly from the target rocks. However, a stronger bias toward refractory clasts in the interior zones of the sheet suggests a higher equilibration temperature and a lower initial content of clasts in these zones. Thermal equilibration of clasts and melt during the first stage of cooling required tens of seconds to a few minutes, whereas completion of crystallization during the second stage required about 1600 more years. Geophysical data suggest the presence of uplifted mafic rocks in the center of the structure and are compatible with an initial transient cavity with a radius of 15 to 22 km and a modeled depth of 6 to 9 km.