The 2011 Tohoku earthquake, tsunami and resulting damage is often referred to as 3.11 after the date on which it took place. Leading to almost 20 000 people dead or missing, a major nuclear disaster and severe economic damage, 3.11 represents the biggest challenge faced by Japan since the end of World War II. Before 3.11, the possibility of a Mw 9 earthquake in this area was not generally recognized, highlighting the need to reassess seismic risk in NE Japan. The large amount of new quantitative data covering a range of disciplines and from onshore and offshore studies makes 3.11 an important case study that can contribute to improving our understanding of tsunamis, including their formation, their effects on coastal regions and the effectiveness of defensive measures old and new. Geological studies have a key role to play in this new phase of tsunami studies and this is the only method available for determining recurrence intervals over timescales of thousands of years. Data from 3.11 have improved our ability to identify sedimentary records of tsunami events and to estimate tsunami size from geological data. More complete databases will provide invaluable information for long-term planning of coastal regions in convergent plate margins.