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 on from the 1998 feature film and focused heavily on FBI federal agents Fox Mulder (David Duchovny) and Dana Scully's (Gillian Anderson) 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".
The season was the first to be filmed in Los Angeles, after production was moved from Vancouver, Canada. This move was done largely on the behest of Duchovny, who wished to be closer to his wife, Téa Leoni. Series creator Chris Carter opposed the move, although series director Kim Manners and Anderson approved of it, although to a less-vocal degree than Duchovny. The first half of the season also saw Mimi Rogers and Chris Owens' characters—Diana Fowley and Jeffrey Spender, respectively—become recurring characters.
Despite debuting with high viewing figures and ranking as the twelfth most watched television series during the 1998–99 television year, the season saw a slight decrease in ratings from the previous one, a trend that would continue until its final year. The season received mixed to positive reviews from television critics; some critics and fans were alienated by the show, due to the different tone taken by most stand-alone episodes after the move to Los Angeles. Rather than adhering to the previous style of "monsters of the week", they were often romantic, humorous, or a combination of both.