The focus of the two temporary seismic networks CYCNET and LIBNET was to monitor the south Aegean region which has the highest seismic activity in Europe. The knowledge of seismotectonics of the volcanic arc of the Hellenic subduction zone poses a number of questions that can best be addressed via an investigation of the spatiotemporal distribution of hypocenters. In order to obtain hypocenters with small location errors and low detection threshold the CYClades seismic NETwork (CYCNET) was installed in the central volcanic arc of the Hellenic subduction zone. Up to 22 stations, equipped with short-period and broadband sensors, were distributed on 17 islands and operating for more than two years starting in autumn 2002. Most islands were equipped with a single seismic station. To decrease the detection threshold at the volcanic centers of Milos and Santorini additional stations were installed there. The combination of short-period and broadband sensors provides data for both seismicity studies and structural investigations. Focussing on the Santorini-Amorgos zone the University of Hamburg (Dahm, T., Hensch, M.) deployed 6 Ocean Bottom Seismometers (OBS)(SANT1-SANT6) near the submarine volcano Columbo for about two month in 2005. In order to better resolve seismic activity in the region of the forearc slivers between the Ptolemy-, Pliny- and Strabo-Trenches south of Crete and to map the subducting African lithosphere in this region as well as the southern termination of the seismogenic zone the LIByan sea the seismic offshore NETwork (LIBNET) was installed. This network consisting of up to 6 simultaneously recording Ocean Bottom Seismometers (OBS) was operated from May 2003 until June 2004 in five subsequent deployment phases. Waveform data are available from the GEOFON data centre, under network code ZZ, and are fully open.