"Unrequited" is the sixteenth episode of the fourth season of the American science fiction television series The X-Files. It was written by Howard Gordon and series creator Chris Carter, and directed by Michael Lange. It originally aired in the United States on February 23, 1997, on the Fox network. The episode is a "Monster-of-the-Week" story, a stand-alone plot which is unconnected to the series' wider mythology. This episode earned a Nielsen rating of 10.9 and was seen by 16.56 million viewers upon its initial broadcast. "Unrequited" received mixed to negative reviews from television critics.

The show centers on FBI special agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) who work on cases linked to the paranormal, called X-Files. In this episode, the murder of a U.S. Army Lieutenant General has Mulder and Scully struggling to stop a seemingly invisible assassin. The two agents soon learn that they are doomed to failure from the start, as the U.S. government is attempting to cover up the existence of American POWs still being kept in Vietnam.

Gordon was inspired to write the episode after viewing an installment of the news series 60 Minutes that dealt with American secret agents the CIA left behind during the Vietnam War. The eventual concept that the assassin could create blind spots came after the writer spoke with his ophthalmologist brother. The entry featured a finished replica of the Vietnam Veterans Memorial, and various Canadian locales substituted for various locations in Washington, D.C.