The major nuclear accident at the Fukushima Daiichi nuclear power plant more than one year ago was the result of a combination of four inter-related factors: site selection, external hazard assessment and site preparation, the utility's approach to risk management, and fundamental reactor design. The reactor accident was initiated by a magnitude 9 earthquake, followed by an even more damaging tsunami. An insufficient tsunami defense-in-depth strategy led to significant core damage in three units and radioactive release to the environment. This paper provides a summary of the sequence of events that led to the accident and current efforts to contain and manage the released radioactivity.