"Triangle" is the third episode of the sixth season of the American science fiction television series The X-Files. It premiered on the Fox network on November 22, 1998. Written and directed by series creator Chris Carter, "Triangle" is a "Monster-of-the-Week" episode, a stand-alone plot which is unconnected to the overarching mythology of The X-Files. "Triangle" earned a Nielsen household rating of 10.8, being watched by 18.20 million viewers in its initial broadcast. The episode generally received positive reviews with many critics commenting on the episode's directing style.

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".