"The Unnatural" is the 19th episode of the sixth season of the American science fiction television series The X-Files, which first aired on April 25, 1999, on the Fox network. Written and directed by lead actor David Duchovny, the episode is tangentially connected to the wider mythology of The X-Files, but narratively functions as a "Monster-of-the-Week" story. "The Unnatural" earned a Nielsen household rating of 10.1, and its first broadcast was watched by 16.88 million people. The episode received positive reviews from critics, and was well-liked by members of the cast and crew, including series creator Chris Carter and co-star Gillian Anderson.

The sixth season of the science fiction television series The X-Files commenced airing on the Fox network in the United States on November 8, 1998, concluding on the same channel on May 16, 1999, and consisted of twenty-two episodes. The season continued from the 1998 feature film and focused heavily on FBI federal agents Fox Mulder and Dana Scully's separation from the X-Files Division and the demise of the Syndicate—a "shadow government" group attempting to cover up the existence of extraterrestrials—in the two-part episode "Two Fathers" and "One Son".