"Fionna and Cake" is the ninth episode of the third season of the American animated television series Adventure Time.

The episode was written and storyboarded by Adam Muto and Rebecca Sugar, from a story by Mark Banker, Kent Osborne, Patrick McHale, and series creator Pendleton Ward.

The concept of Fionna and Cake was based on sketches that series' character designer and storyboard revisionist Natasha Allegri made.

Two sequels to the episode—"Bad Little Boy" and "The Prince Who Wanted Everything"—were produced during the show's fifth and sixth season, respectively as well as a comic book miniseries titled Adventure Time with Fionna and Cake published by kaBOOM along with a spin-off series featuring the characters titled Adventure Time: Fionna and Cake.

A drop of water lands on her shoulder, she looks up to see the real Prince Gumball trapped inside a giant icicle on the ceiling.

The episode quickly reveals itself to be a fanfiction story created by the Ice King, who is reading it to an imprisoned Finn and Jake.

"Fionna and Cake" was written and storyboarded by Rebecca Sugar and Adam Muto from a story developed by Mark Banker, Patrick McHale, Osborne, and series creator Pendleton Ward; it was directed by Larry Leichliter.

The genesis for the episode were drawings that character designer and storyboard revisionist Natasha Allegri posted online.

[11] Sugar intended "Fionna and Cake" to both be "a jab [and] a huge celebration of, [sic] the feeling of being fan" and "allowing something completely ridiculous to make your heart tighten".

[12] Sugar and Muto significantly changed the story from its original outline, as the very first version of the episode did not feature the Ice Queen, the ball, or the crystal sword.

[15] Tyler Foster of DVD Talk praised the episode for its creativity and complimented the entry's humor and its message to girls.

Club called the "Fionna and Cake" one of "the most fascinating aspects of the Adventure Time craze" in a review of the fifth-season episode "Bad Little Boy".

He wrote that "'Fionna and Cake' was reminiscent of the series' earlier episodes, in regard to its bright animation, well-paced plot, music, its successful blend of fantasy action and comedy, and its focus on character-based drama.