The Irish Seismological Lithospheric Experiment (ISLE 2002) has been designed to investigate the deep lithospheric and asthenospheric structure across the late-Caledonian Iapetus Suture Zone in southern Ireland. The project is a collaboration between the Dublin Institute for Advanced Studies (DIAS), Ireland, and the Geophysical Institute (GPI) of the University of Karlsruhe, Germany. This is the first passive teleseismic experiment conducted in Ireland, building upon a large body of earlier work on the crustal structure offshore and onshore Ireland, based on controlled source seismics and potential field studies. In the geological past, during Cambrian and Ordovician times, the north and south of Ireland were separated by the Iapetus Ocean and belonged to two different continental blocks. Continental drift of these pre-Caledonian continents, Laurentia in the northwest and Eastern Avalonia in the southeast, led to the closure of the Iapetus Ocean during late Ordivician and Silurian times. When the former ocean closed (early Devonian), the oceanic lithosphere was subducted subsequently forming the Caledonian orogenic belt. Hence, the Iapetus Suture Zone (ISZ), which extends approximately from the Shannon Estuary in the west of Ireland across the Irish Midlands toward the northeast (grey band in Figure 1), resulted from the amalgamation in the three-plate configuration of Laurentia and Baltica with Avalonian.