Additionally, the Simpsons franchise celebrated its 20th anniversary, as it has been on the air since April 1987, beginning with shorts on The Tracey Ullman Show.

Season 18 included guest appearances by Metallica, Tom Wolfe, Gore Vidal, Michael Chabon, Ludacris, Jonathan Franzen, Fran Drescher, The White Stripes, Kiefer Sutherland, Mary Lynn Rajskub, Richard Lewis, Dr. Phil, Elvis Stojko, Natalie Portman, Jon Lovitz, Betty White, Eric Idle, Sir Mix-a-Lot, Stephen Sondheim, Ronaldo, Meg Ryan, Andy Dick, Peter Bogdanovich, James Patterson and others.

Bart gets a drum kit to work out his aggression after being a nuisance at the funeral of Homer's Vegas wife and becomes top pick for a local jazz band, a position that the saxophone-playing Lisa has been going after for years.

Wells' War of the Worlds, the citizens of Springfield in 1938 ignore a real alien invasion set up by Kang and Kodos.

When Bart agrees to enlist in the army when he turns 18, Marge sends Homer to the recruitment center to undo it.

After Gil Gunderson gives Lisa a Malibu Stacy doll reserved for Mr. Costington's daughter, he gets fired as a mall Santa and the Simpsons invite him to dinner and to stay the night.

However, when he drives to North Haverbrook, he is then engaged with a girl named Darcy who ropes Bart into getting married after declaring that she is pregnant.

Declan Desmond returns as he shows a documentary about Springfield's current adult population as children, discussing their future aspirations and meeting up with Homer to see if he followed his dreams.

Lisa becomes a tutor for Cletus Spuckler's children after Principal Skinner bars them from enrolling in Springfield Elementary.

Meanwhile, Bart ends up in therapy after scaring his peers with stories of a school chef notorious for cooking children.

When Grampa gets kicked out of the retirement castle thanks to Homer declaring bankruptcy and discovering that bankruptcy laws have changed, Grampa falls in love with Marge's sister Selma, prompting sworn enemies Homer and Patty to team up to break them up.

Tasting success and seeing money to be made, Homer takes to the streets as one of the paparazzi, capturing Springfield's celebrities at their worst.

When Homer gets lost in a cornfield maze, Santa's Little Helper rescues him and becomes a local hero, which prompts the Simpson family to enroll him in Police Dog Academy, where he dons a new and more stern personality.

However, he becomes jaded when he catches Snake Jailbird, who is released on a technicality, and bites Bart, causing the family to give him away.

When he shows his snake at school, and it causes a hazardous situation, Santa's Little Helper comes to save Bart and returns to the family.

Due to Ned Flanders' meddling, Kent Brockman gets in trouble for blurting a horrible curse word during a soft-news interview about Homer winning Phineas Q. Butterfat's 1,000,000th ice cream cone, and gets fired for allegedly being a cocaine addict.

[26] This season included the 400th episode of the series and marked the 20th anniversary of the Simpson characters' debut on The Tracey Ullman Show.

"[28] At the 35th Annie Awards, Alf Clausen and Michael Price won the award for "Best Music in an Animated Television Production" for "Yokel Chords" while Ian Maxtone-Graham and Billy Kimball won "Best Writing in an Animated Television Production" for "24 Minutes"[29] Jeff Westbrook won a WGA Award for "Kill Gil, Volumes I & II"[30] while Matt Selman was nominated for "The Haw-Hawed Couple" and John Frink received a nomination for "Stop, or My Dog Will Shoot!".

[35][36] Series showrunner Al Jean reported in April 2015 that The Simpsons would no longer see home media releases after the seventeenth season, claiming an inability for DVD sales to keep up with the rise in streaming and downloads, as well as a boom in FXX reruns, and Fox's on-demand video service, FXNOW.

On Saturday, July 22, 2017, it was announced during the 2017 San Diego Comic-Con panel that, due to fan demand, the eighteenth season DVD would be released after all on Tuesday, December 5, 2017, in the United States and Canada by 20th Century Fox Home Entertainment, ten years after it had completed broadcast on television.