Seismic, magnetic, and geologic data are used to provide constraints on gravity models of the crust from southeastern Norway into the Skagerrak. Seismic data indicate that the Moho rises from more than 39 km under central Norway to approximately 30 km under the Skagerrak and that a basin with about 5 to 6 km of sediments is present in the Skagerrak. Magnetic data show a maximum depth of 6 km to magnetic basement in the sedimentary basin, and characteristic magnetic anomalies are found over basement along the coast and under the Skagerrak. The Great Friction Breccia fault zone, separating migmatitic and supracrustal rocks along the southeast coast, is a major tectonic feature on land. Bouguer gravity anomalies increase from slightly negative values northwest of the breccia zone to as high as +50 mgal along the coast and offshore. Major features of this interpretation are the following: (A) recognizable supracrustal rocks are more mafic than underlying mobilized migmatites, (B) a probable crustal low-velocity zone is formed by the above compositional inversion, (C) intrusive granites in the supracrustal rocks may be formed by anatexis and diapiric uprise of the migmatites, (D) the Great Friction Breccia is a major tectonic feature, and (E) continuation of the Oslo Graben and associated igneous rocks under the Skagerrak seems likely.