The origin of the Ionian Sea lithosphere and the deep structure of its margins remain a little investigated part of the Mediterranean Sea. To shed light on the plate tectonic setting in this central part of southern Europe, R/V METEOR cruise M111 set out to acquire deep penetrating seismic data in the Ionian Sea. M111 formed the core of an amphibious investigation covering the Ionian Sea and island of Sicily. A total of 153 OBS/OBH deployments using French and German instruments were successfully carried out, in addition to 12 land stations installed on Sicily, which recorded the offshore air gun shots. The aim of this onshore-offshore study is to quantify the deep geometry and architecture of the Calabria subduction zone and Ionian Sea lithosphere and to shed light on the nature of the Ionian Sea crust (oceanic crust vs. thinned continental crust). Investigating the structure of the Ionian crust and lithospheric mantle will contribute to unravel the unknown ocean-continent transition and Tethys margin. Analyzing the tectonic activity and active deformation zones is essential for understanding the subduction processes that underlie the neotectonics of the Calabrian subduction zone and earthquake hazard of the Calabria/Sicily region, especially in the vicinity of local decoupling zones.