The Boxing Day Tsunami in 2004 triggered various international efforts focused on tsunami early warning for the Indian 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 considerably. The warning system architecture has been specifically addressed in two complementary projects: firstly, German-Indonesian Tsunami Early Warning System (GITEWS), funded by the German Federal Ministry of Education and research EMBF, 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).