It doesn't seem like a likely pairing, but a cameo in X-Files season 5 canonically places the show within the Law & Order universe. To be fair,The X-Files and Law & Order do have some things in common. At their core, both are crime procedural dramas, albeit with monsters and aliens involved on The X-Files, and elements of legal drama thrown in on Law & Order. They're also both long-running programs, although The X-Files' 11-season run certainly is dwarfed by the over 20 seasons of Law & Order and its first spinoff SVU.
Beyond that though, there likely isn't that much crossover between diehard fans of The X-Files' mix of investigative sci-fi horror and diehard fans of Law & Order's gritty look at the criminal justice system. The X-Filesdefinitely isn't a stranger to weird crossovers though, as Mulder and Scully once got animated for a trip to Springfield on The Simpsons, and even starred in an in-universe episode of fellow long-running FOX series Cops.
Related: X-Files: Why David Duchovny Nixed Gillian Anderson's Californication Cameo
The fateful episode that forever bound The X-Files and the Law & Order-verse together came in season 5's «Unusual Suspects,» which primarily served as a flashback story detailing how Mulder first became acquainted with The Lone Gunmen trio. The Gunmen are arrested and shortly after, are interrogated by a very familiar cop—Detective John Munch (Richard Belzer), a character best known forLaw & Order: SVU. Munch was a regular on SVU for its first 15 seasons.
Perhaps the oddest thing about The X-Files existing within the Law & Order universe is that when «Unusual Suspects» aired in 1997, including Belzer's Munch wasn't actually meant to be a Law & Order crossover. At that time, Munch was still a
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