"The War of the Worlds" was a Halloween episode of the radio series The Mercury Theatre on the Air directed and narrated by Orson Welles as an adaptation of H. G. Wells's novel The War of the Worlds (1898) that was performed and broadcast live at 8 pm ET on October 30, 1938, over the CBS Radio Network. The episode is famous for inciting a panic by convincing some members of the listening audience that a Martian invasion was taking place, though the scale of panic is disputed, as the program had relatively few listeners. The episode begins with an introductory monologue based closely on the opening of the source novel, after which the program takes on the format of an evening of typical radio programming being periodically interrupted by news bulletins. The first few bulletins interrupt a program of live music and are relatively calm reports of unusual explosions on Mars followed by a seemingly unrelated report of an unknown object falling on a farm in Grovers Mill, New Jersey.

The crisis escalates dramatically when an on-scene reporter at Grovers Mill describes creatures emerging from what is evidently an alien spacecraft. The aliens employ a heat ray against police and onlookers, and the radio correspondent describes the attack in increasing panic until his audio feed abruptly goes dead. This is followed by a rapid series of news updates detailing the beginning of a devastating alien invasion and the US military's futile efforts to stop it. The first portion of the episode climaxes with a live report from a rooftop in Manhattan, from where a correspondent describes citizens fleeing from poison smoke released by towering Martian "war machines" until he coughs and falls silent. Only then does the program take its first break, about thirty minutes after Welles's introduction.