The East Greenland Caledonian orogen can be divided into distinct structurally bound geological domains composed of Archean to Lower Paleozoic lithostrati graphic and lithodemic components derived from the eastern margin of Laurentia. These domains originally evolved as major westward-displaced thrust units in the overriding plate during the collision with Baltica. The western border of the 1300-km-long and up to 300-km-wide segment of the orogen preserved onshore in East Greenland is thrust against the rocks of the Laurentian craton and is largely concealed beneath the Inland Ice. A foreland-propagating thrust pile is well-preserved in the extreme north of the orogen (79°N-82°N), and in the southern half (70°N-76°N), with lesswell- preserved remnants in the western nunataks of the intervening region. Between 76°N and 81°N, the outer coastal region is dominated by high-grade Paleoproterozoic orthogneisses that were reworked during the Caledonian orogeny; most of this region is characterized by the presence of eclogitic mafic enclaves, which testify to exhumation from depths in excess of 50 km in late Caledonian time. Caledonian granites are confined to the southern orogen (70°N-76°N), where they intrude rock units now contained within the upper thrust sheet. Devonian continental basins are conspicuous in the southern part of the orogen and occur offshore farther north; their deposition can be linked to syn- to late-orogenic extension. Carboniferous and younger rocks are exposed onshore in the extreme north of the orogen (80°N-81°N) and are widespread in the south between 71°N and 75°N.