Tsunamis are caused by geological processes, such as earthquakes, landslides, or volcanic eruptions, that displace large volumes of ocean water. Large-magnitude, subduction zone earthquakes, where two plates in the ocean push into each other, are the most common source of the recent large tsunamis. Submarine landslides, sometimes triggered by earthquakes, and coastal or submarine volcanoes also cause tsunamis. This chapter describes 10 modern and historic tsunami events that were significant in terms of their size, impact, extent, and/or triggering mechanisms. Each tsunami event is described using four different categories: (1) tsunami generation; (2) tsunami size, and extent (3) impact of the event at the local, regional and, where applicable, global scales; and (4) lessons learned in the aftermath of the event. The case studies are grouped according to the tsunamigenic source: earthquake (2004 Indian (SumatraeAndaman) earthquake, 2011 Tohoku earthquake, 1964 Alaska earthquake, 1960 Valdiviaearthquake, 1946 Aleutian Island earthquake, 1908 Messina-Reggio earthquake, 1755 Great Lisbon earthquake), landslide (Storegga Slides 30,000 and 7,200e7,000 YBP, Papua New Guinea, 1998), and volcano (Krakatoa 1883).