Sein und Zeit (The X-Files)

"Sein und Zeit" is the tenth episode of the seventh season of the science fiction television series The X-Files. The German language title directly references Martin Heidegger's best known work, translated as "Being and Time" in English. It premiered on the Fox network on February 6, 2000, in the United States. The episode was written by Chris Carter and Frank Spotnitz, and directed by Michael Watkins. The episode helped to explore the series' overarching mythology. "Sein und Zeit" earned a Nielsen household rating of 8.4, being watched by 13.95 million people in its initial broadcast. It received mixed to positive reviews from 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. Mulder is a believer in the paranormal, while the skeptical Scully has been assigned to debunk his work. In this episode, Mulder becomes obsessed with a number of children who have vanished while investigating the bizarre disappearance of a young girl from her home. In the meanwhile, Scully fears that he is emotionally involved due to his sister's disappearance 27 years earlier. Her fears are heightened when Mulder's mother dies, apparently of suicide.

"Sein und Zeit" was written as the first part of a two-part arc that would eventually reveal what had happened to Samantha Mulder. Executive producer Frank Spotnitz later noted that the episode bore stylistic similarities to the fourth-season episode "Paper Hearts". Several production issues plagued the episode, including the arrest of one crew member who was accused of possible kidnap, and the lack of money needed for the faux newscast scene at the end of the episode.