The 2011 Tohoku earthquake generated a tsunami that caused severe damage including 20,000 casualties in Japan. The tsunami also affected other Pacific coasts, including the Kuril Islands, the USA, French Polynesia, the Galapagos Islands, Australia, and New Zealand. This volume contains an introduction and 21papers, mostly presented at the 25th International Tsunami Symposium held 1-4 July 2011, only four months after the tsunami. They report seismological aspects of the event related to the tsunami warning, the tsunami impacts and effects in Japan and around the Pacific, analyses of instrumental tsunami data and modelling.