The world's most powerful earthquake in forty years occurred the morning of December 26, 2004 under the Indian Ocean off the Indonesian island of Sumatra. A tsunami was generated which killed nearly 220,000 people in eleven countries around the Indian Ocean from Sumatra, Thailand, India and Sri Lanka to Somalia on the Horn of Africa. The tsunami caused waves which were recorded as far away as Argentina and France. Various aspects of this event will be discussed along with a brief description of the tsunami warning system and mitigation efforts on the west coast. In addition, research conducted over the years at Caltech dealing with the generation, propagation and coastal effects of tsunamis will be discussed.