Three Mile Island is a nuclear power facility located on an island in the Susquehanna River near Middletown, Dauphin County, Pennsylvania. On March 28, 1979, equipment failure and human error led to a partial meltdown and release of radioactive gases, the worst nuclear accident in U.S. history. Unit 2, where the accident took place, has never reopened, but power continues to be generated in Unit 1. Although various studies have found no health effects among TMI employees or the surrounding communities, events at TMI have led to improvements in the training of reactor operators and emergency responders, as well as increased regulation of the nuclear power industry. This guide provides links to information sources on the history and current status of Three Mile Island from industry, health, social, and other perspectives.