Throughout the 1300 km long East Greenland Caledonides, the western exposed marginal thrusts overlie foreland rocks of latest Neoproterozoic–Early Palaeozoic age, mainly exposed in tectonic windows. In the western, 100–130 km wide, marginal thrust belt, the thrust planes outlining the windows appear to follow long flats developed in Lower Palaeozoic carbonates. East of the marginal thrust belt, thrust inclinations steepen, and by implication the remaining part of the Caledonian orogen extending eastwards to the present Atlantic Ocean coast is allochthonous and thick-skinned. The contrast between the restricted Neoproterozoic–Lower Palaeozoic foreland succession and the very thick and almost continuous sedimentation of the allochthonous Neoproterozoic Eleonore Bay Supergroup–Tillite Group–Cambro-Ordovician sequence of the fjord zone of East Greenland confirms the presence of distinct N–S trending facies belts on the northwestern passive margin of Iapetus. Comparisons with the Caledonides of Northwest Scotland, which may originally have lain as little as 500 km south of the East Greenland Caledonides, provide further clues to the understanding of Neoproterozoic–Early Palaeozoic basin geometry on this sector of the developing Iapetus margin. The areas of the Laurentian margin represented in the foreland windows of East Greenland were inboard of Neoproterozoic rifting but, with respect to the Torridonian basins of Northwest Scotland, the Eleonore Bay Supergroup succession must have been laid down further outboard. Similarly the Lower Palaeozoic developments of the foreland of Northwest Scotland are thicker than the equivalent foreland sequences of East Greenland, but much thinner than the allochthonous East Greenland Cambro-Ordovician succession.