The Boxing Day Tsunami in 2004 triggered various interna-tional efforts focused on tsunami early warning for the In-
dian Ocean Basin. Stimulated by developments in the field of tsunami science and information and communications technology (ICT), the technological concepts of tsunami early warning systems (TWS) have been improved consid-
erably. The warning system architecture has been specifi-cally addressed in two complementary projects: firstly, Ger-
man Indonesian Tsunami Early Warning System (GITEWS), funded by the German Federal Ministry of Education and
Research BMBF, and, secondly, Distant Early Warning System (DEWS), a European project co-funded under FP6. The development is continued by the FP7 large-scale integrated project Collaborative, Complex and Critical Decision Support in Evolving Crises (TRIDEC).