Most of the world’s earthquakes and tsunamis occur in the Pacific Ocean and its marginal seas. On average, the Pacific is struck by a locally damaging tsunami every year or two, and by a major Pacific-wide tsunami a few times each century. Over the past three years (2009–2011), the Pacific witnessed three destructive and deadly tsunamis that each placed PTWS (Pacific Tsunami Warning and Mitigation System) countries in various levels of warning for distant tsunamis. Locally, five countries were impacted nearly immediately with people having only 10 to 30 minutes before the first large waves hit. A Pacific-wide tsunami exercise is an effective tool for evaluating the readiness of the PTWS and to identify changes that can improve its effectiveness. The first Pacific-wide exercise, “Exercise Pacific Wave 06” (IOC/INF-1244), was carried out on 16 and 17 May 2006 using Philippines and Chile tsunami sources. The second exercise “Exercise Pacific Wave 08” (IOC/2008/TS/82), was carried out from 28 to 30 October 2008 using a northeast Japan source. At the Twenty-fourth Session of the ICG/PTWS held in Beijing, China, from 24 to 27 May 2011, Member States reviewed the proposal of the PTWS Exercise Task Team and approved the conduct of Exercise Pacific Wave 11 (Exercise Pacific Wave 11) on 9 and 10 November 2011 as a multi-scenario exercise to allow countries to improve their readiness for local and regional tsunamis (ICG/PTWS-XXIV/3, Rec. 3). Exercise Pacific Wave 11 will be held on 9 and 10 November 2011, and will involve multiple scenarios, played out in real time, to allow all Pacific countries to select and exercise a regional/local source tsunami event.