On Friday, March 11, 2011, one of the largest earthquakes in the recorded history of the world occurred on the east coast of northern Japan. This earthquake also generated a major tsunami, causing nearly 20,000 deaths. Electricity, gas and water supplies, telecommunications, and railway service were all severely disrupted and in many cases completely shut down. These disruptions severely affected the Fukushima Daiichi nuclear power plant, causing a loss of all on-site and off-site power and a release of radioactive materials from the reactors. The leadership of the American Nuclear Society commissioned the American Nuclear Society Special Committee on Fukushima to provide a clear and concise explanation of what happened during the Fukushima Daiichi accident, and offer recommendations based on lessons learned from their study of the event. The American Nuclear Society, a professional organization of 11,600 nuclear science and technology professionals, has a strong tradition of advancing nuclear safety, and the Special Committee on Fukushima was organized to further its members' interests in this important professional obligation.