The ninth season of the American animated television series The Simpsons originally aired on the Fox network between September 1997 and May 1998, beginning on Sunday, September 21, 1997, with "The City of New York vs. Homer Simpson". Mike Scully served as showrunner for the ninth production season.^[1] The ninth broadcast season contained three episodes with 4F-series production codes, indicating that they were hold-over episodes from production season eight, and two episodes with 3G-series production codes, which are not explicitly confirmed to be part of any production season but are speculated to be relabeled 3F-series (seventh production season) episodes.^{[2][3][4][5][6][7][8]} This makes it the first broadcast season to include holdover episodes from two previous production seasons.

Season nine won three Emmy Awards: "Trash of the Titans" for Primetime Emmy Award for Outstanding Animated Program (for Programming Less Than One Hour) in 1998,^[9] Hank Azaria won "Outstanding Voice-Over Performance" for the voice of Apu Nahasapeemapetilon,^[10] and Alf Clausen and Ken Keeler won the "Outstanding Music and Lyrics" award.^[11] Clausen was also nominated for "Outstanding Music Direction" and "Outstanding Music Composition for a Series (Dramatic Underscore)" for "Treehouse of Horror VIII".^[9] Season nine was also nominated for a "Best Network Television Series" award by the Saturn Awards and "Best Sound Editing" for a Golden Reel Award.^[11]

The Simpsons 9th Season DVD was released on December 19, 2006, in Region 1, January 29, 2007, in Region 2 and March 21, 2007, in Region 4. The DVD was released in two different forms: a Lisa-shaped head, to match the Maggie, Homer and Marge shaped heads from the three previous DVD sets, and also a standard rectangular shaped box. Like the previous DVD sets, both versions are available for sale separately.

This is the last season to feature the character Lionel Hutz, voiced by Phil Hartman. Following Hartman's death on May 28, 1998, Hutz was retired along with Hartman's other recurring character Troy McClure; his final speaking role as Hutz was five months earlier, in the episode "Realty Bites", and has since occasionally appeared as a background character.

The ninth season is considered by some fans and critics to be the end of the Golden Age of The Simpsons. Alasdair Wilkins of The A.V. Club said: "From here on out, we're in The Simpsons' decline phase, though there's plenty of room to disagree just how stark the drop-off actually was."^[12] On Rotten Tomatoes, the ninth season of The Simpsons has a 67% approval rating based on 6 critical reviews.^[13]

The second episode of the ninth season, "The Principal and the Pauper" is often regarded as one of the most controversial episodes of the entire series. Many fans and critics reacted negatively to the revelation that Principal Skinner, a recurring character since the first episode who had undergone much character development, was an impostor. The episode has been criticized by series creator Matt Groening, and by Skinner's voice actor Harry Shearer. In his 2004 book Planet Simpson, Chris Turner describes the episode as the "broadcast that marked [the] abrupt plunge" from The Simpsons' "Golden Age", which he says began in the middle of the show's third season. He calls the episode "[one of] the weakest episodes in Simpsons history", and adds, "A blatant, continuity-scrambling plot twist of this sort might've been forgivable if the result had been as funny or sharply satirical as the classics of the Golden Age, but alas it's emphatically not." Turner notes that the episode "still sports a couple of virtuoso gags", but says that such moments are limited.^[14]

In July 2007, in an article in The Guardian, Ian Jones argues that the "show became stupid" in 1997, pointing to the episode as the bellwether. "Come again? A major character in a long-running series gets unmasked as a fraud? It was cheap, idle storytelling", he remarks.^[15] In a February 2006 article in The Star-Ledger, Alan Sepinwall and Matt Zoller Seitz cite the episode when asserting that the quality of The Simpsons "gets much spottier" in season nine.^[16] Alan Sepinwall observes in another Star-Ledger article, "[The episode] was so implausible that even the characters were disavowing it by the end of the episode."^[17] Jon Hein, who coined the term "jumping the shark" to refer to negative changes in television series, writes in Jump the Shark: TV Edition, "We finally spotted a fin at the start of the ninth season when Principal Skinner's true identity was revealed as Armin Tamzarian."^[18] James Greene of Nerve.com put the episode fifth on his list "Ten Times The Simpsons Jumped the Shark", calling it a "nonsensical meta-comedy" and arguing that it "seemed to betray the reality of the show itself".^[19] On the 25th anniversary of the episode airing, Fatherly looked back negatively at the episode, described the plot twist as the moment the show stopped being perfect, saying: "It wasn't funny, it was just mean, and the ending of the episode inadvertently made you complicit in its viciousness. Ultimately, the citizens of Springfield decide to force things back to normal by tying the real Skinner to a departing train and legally declaring that Tamzarian's theft of an entire life is fine. And, well, yeah we as the viewers wanted things to go back to normal once the episode was over, but…this was just heartless."^[20]

In terms of households, the show ranked just outside the Top 30, coming in at No. 32 with a 9.3 household rating and a 15 percent audience share.^[64] However, in terms of total viewers, the show ranked within the Top 20, coming in at No. 18 for the season, (tying with Dateline Tuesday) and being watched by an average of 15.3 million viewers per episode.^[65]

The DVD boxset for season nine was released by 20th Century Fox in the United States and Canada on December 19, 2006, eight years after it had completed broadcast on television. As well as every episode from the season, the DVD release features bonus material including deleted scenes, animatics, and commentaries for every episode. As with the two preceding seasons, the set was released in two different packagings: A "Collector's Edition" plastic packaging molded to look like Lisa's head, and a standard rectangular cardboard box featuring Lisa with a backstage pass to a show at a club.^[66] The menus continue the same format from the previous four seasons, and the overall theme is various characters waiting in line at a club.

• List of The Simpsons episodes