On November 18, 1978, cult leader Reverend Jim Jones and his followers die in South America. In all 909 people are killed, the largest mass murder-suicide of US citizens in history.

"Jonestown" was the informal name for the Peoples Temple Agricultural Project, an intentional community in northwestern Guyana formed by the Peoples Temple led by an American, Jim Jones. It became internationally notorious when on November 18, 1978, 918 people died in the settlement, at a nearby airstrip, and in Georgetown (Guyana's capital). The name of the settlement became synonymous with the incidents at those locations.

A total of 909 Temple members died in Jonestown, all but two from apparent cyanide poisoning, in an event termed "revolutionary suicide" by Jones and some members on an audio tape of the event and in prior discussions. The poisonings in Jonestown followed the murder of five others by Temple members at a nearby Port Kaituma airstrip. The victims included United States Congressman Leo Ryan. Four other Temple members died in Georgetown at Jones' command.

To an extent, the actions in Jonestown were viewed as a mass suicide; some sources, including Temple survivors, consider the event to be a mass murder. It was the largest such event in modern history and resulted in the largest single loss of American civilian life in a non-natural disaster until the events of September 11, 2001.