Deep seismic refraction data were gathered along the East Greenland rifted margin between the Jan Mayen and Greenland fracture zones (72°N 77°N) in 2003. Investigations of the deep structure of the continental margin provide key constraints on the formation of the margin and its structural evolution during and after Late Cretaceous - Early Tertiary rifting and continental break-up. Regional P-wave velocity models were inferred from forward travel-time modeling of land stations and ocean bottom hydrophone (OBH) recordings along four seismic refraction profiles. For the first time, transects off East Greenland provide a full insight into the crustal architecture of the transition from continental to oceanic crust. An overall view shows significant variations in the crustal structure along the margin. These include a decrease in the thicknesses of the magmatic underplate towards the north, and a widening of the COT in the south. P-wave velocities of the underplated material range between 7.1 and 7.4 km/s. The horizontal extent is widest (~200 km) along the southern profiles north of the Jan Mayen Fracture Zone and decrease further north towards the Greenland Fracture Zone. The maximum thickness of the underplated material is 15 - 16 km. From earlier investigations, a southward decrease in the amount of underplated material is observable and near Scoresby Sund no underplating was identified. Furthermore, the P-wave velocity models reveal a ~120 km wide continent ocean transition zone (COT), based on an interpretation of the extent of continental sediments and the lateral increase of velocities in the crustal layers. Excess magmatism must have been present during a long-term rifting process, accompanying the wide extension of the continental crust and giving rise to the voluminous magmatic underplating. This interpretation and the crustal variations along the margin could be consistent with a model featuring rift propagation from north to south. Additionally a comparison of P-wave velocity models of the East Greenland Margin and Vøring Margin reveals significantly asymmetric crustal architectures. The voluminous magmatic underplating and asymmetrical conjugate margins formations are evidence for complex pre- and syn-rift processes.