As recently experienced in Japan, tsunamis represent one of the most important risk sources for low-lying coastal zones and their inhabitants, due to both their destructive potential and their unpredictability. The tsunami of 26 December 2004, which hit the Andaman Sea coast of Thailand, caused thousands of casualties, disrupted economies and social well-being in many coastal communities and resulted in drastic changes of the coastal zone and marine environment. This tsunami also revealed a gap in scientific knowledge, beginning from the triggering of tsunamis offshore to the various impacts to the natural environments on the shelf, coastal areas and on land and to the economic and social system consequences. An interdisciplinary Thai–German research project ("TRIAS" – Tracing Tsunami Impacts On- and Offshore in the Andaman Sea Region) was launched, addressing the following topics:

• Where and how can tsunamis be triggered in the Andaman Sea and what are the indicators of tsunami-generating mechanisms?
• How often have tsunamis struck the coast of the Andaman Sea in the recent past and how does sedimentary evidence on- and offshore look?
• What are the impacts of tsunamis on the seafloor morphology, sediment cover and on the marine and littoral ecosystems?
• How is tsunami wave energy attenuated in the nearshore zone, beachfront and hinterland, and how is this attenuation influenced by the presence of natural barriers such as coastal forests and artificial barriers?
• What factors determine the tsunami-related vulnerability of low-lying coastal areas, their population, communities and economies?
• What kind of socio-economic, institutional and/or other factors make coastal societies or communities resilient against tsunami impacts, and how can risk management, including early warning, be improved to prevent/mitigate future tsunami disasters along coasts?

The questions above provided a feasible basis for addressing key issues of tsunami research. While in the offshore domain natural processes dominate, towards onshore and especially on-land anthropogenic influences increase and trigger the vulnerability. Consequently, individual research groups have established a research network to contribute to the enhancement of the region's ability to cope with tsunami risks.

The objective of this special issue is to complement individual research issues in such a way that a clear picture can be drawn about the destructive forces and processes of the 2004 tsunami and past tsunamis and to elaborate and to suggest measures on how to avoid or mitigate future tsunami impacts and destructions.