Rotating Protagonist

When a series with an ensemble cast has each episode focus on a different character. In other words, a series where every episode is a different character's Day In The Limelight.

Not to be confused with Limelight Series (where the focus stays on an ensemble of previously minor characters). Compare Plot Tailored to the Party, where the overarching story is designed to place each character into the spotlight sooner or later (Rotating Protagonist is more episodic), and Switching POV, where we see different characters' perspectives rather than just them.

If all these stories are happening simultaneously, but shown in different episodes, it's Four Lines, All Waiting.

Not to be mistaken for Everything's Better with Spinning.

Anime and Manga

 * Boogiepop Phantom does this.
 * Paranoia Agent does this for almost every episode.
 * Bokurano does this. Character arcs may last two or three episodes instead of just one, but the principle is the same.
 * Higurashi no Naku Koro ni changes protagonists every arc.
 * Soul Eater, particularly the first three episodes/chapters which introduced each of the three main meisters and their partners (Soul and Maka first, followed by Black Star and Tsubaki and finally Death The Kid and the Thompson sisters). They then got a few Monster of the Week episodes each before the main plot kicked in.
 * Durarara!! does this throughout, though characters do repeat and some episodes aren't about any one in particular.

Comic Books

 * The Brave and the Bold: every month Batman would team up with a new hero. The tradition is carried on in a modern Brave and the Bold series, where every issue features two different heroes or groups working together.
 * Marvel had a counterpart to the above in the original Marvel Team-Up, where heroes would join forces with Spider-Man, and Marvel Two-in-One, where the Thing would have a new partner every issue. As with The Brave and the Bold, a modern MTU series dropped the superstar regular angle and featured new team-ups every time. However, the latest incarnation of the series is Deadpool Team Up, which naturally features the eponymous anti-hero alongside the issue's guest star. Deadpool Team-Up is notable for primarily featuring more obscure characters such as U.S. Archer and It, the Living Colossus. There was also the Marvel Age Supervillain Team-Up, which featured Dr. Doom teaming up with a different supervillain and/or team each issue. The Sinister Six, the Circus of Crime, the (original) Masters of Evil, Magneto...
 * DC's Great Ten miniseries did this - every issue focused on a different member of the titular team. Since the series was cut short due to weak sales, Mother of Champions and Socialist Red Guardsman shared the last one.
 * Marvel Comics' Solo Avengers and DC Comics' Teen Titans Spotlight showcased various members who didn't already have their own series. However, during the former's first year or so, the rotating protagonist in question would star the issue's back-up feature, as Hawkeye was the star of the lead feature.
 * The first six issues of Marvel Comics' Young Avengers each focus on a different member of the team.
 * Heroic Publishing's Champions series mostly uses this kind of format.
 * This is the hook for the latest version of Heroes for Hire: Misty Knight uses her contacts to "maximize the potential of [her] address book", calling in favors from different heroes in every issue. The only constant besides Knight herself is Paladin.

Fan Works

 * In the Vocaloid Fanfic Good Night, nearly the entire cast trade off the narration role. In the order of doing so for the first part,.

Film

 * The Jurassic Park films. In the first film, the main characters are Grant, Ellie, Ian, Hammond, and the kids. In second film, Ian is the main character, Hammond and the kids get cameos, and there is a new set of supporting characters. In the third film, Grant is the main character again, Ellie has a minor role, and there is yet another new set of supporting characters.

Literature

 * In Catch-22, Yossarian is the protagonist, but every chapter is titled and focused on a different character (Milo gets three), and Yossarian is often Out of Focus for long stretches.
 * Each chapter in Kristine Kathryn Rusch's Fay novels concentrates on a different character.
 * The Valley of Horses alternates chapters about Ayla and Jondalar until they meet; it's third person narration.
 * In Tamora Pierce's Circle of Magic series, each of the books focuses on one of the four main characters as they live together, learn magic, and become a family, though each book also features scenes from the perspectives of other characters and their own subplots. The second series, The Circle Opens follows the same format, except the characters are four years older and leave to go travel with their teachers. The latest book, The Will of the Empress is the only one save Sandry's Book which deals with each of the four characters relatively equally.
 * Harry Turtledove's Alternate History novels use this trope to explore different aspects of the world, e.g. a war may be narrated from the perspective of officers and grunts and civilians on different sides. Each chapter includes multiple passages centered around different viewpoint characters.
 * The Animorphs books follow a pattern to determine who the protagonist is. Originally the Token Non Humans, Ax and Tobias, only got half as many books because it was assumed they would be less popular; it turned out to be quite the opposite, however, and the pattern eventually changed.

Live-Action TV

 * Lost may be the most famous example, with almost every episode focusing on a different member of the ensemble cast's flashbacks,
 * Skins combines this with Idiosyncratic Episode Naming: every episode is named after the character that episode is focused on. It even introduces a new cast every two years.
 * As If, the proto-Skins, did this too.
 * Degrassi fits this to a T. The limelight focuses on the characters on the A plot and minorly on the B plot, and the other characters are barely even mentioned.
 * Misfits also does this.
 * The 2004 version of Battlestar Galactica switched focus fairly regularly.

Video Games

 * Mass Effect 2 is like this: each character on your crew gets an (optional, but skip it at your own risk) personal loyalty mission, which is custom-tailored to their combat style and inconspicuously reveals enough of their backstory and personality to make you care about them.
 * Final Fantasy IV: The After Years
 * Final Fantasy VI as well; in the first half of the game the story frequently switches from one character to the next, and there is no clear protagonist (though Dissidia more or less confirmed it was Terra).
 * Final Fantasy XIII switches between at least three groups of main characters all the time, mixing them up every now and then to let each one to interact with every other. It also loves to shift the leader role (the only character you control in combat) about, making sure you don't get too comfortable with any given combination of skills and classes.
 * Odin Sphere. Each of the first five "books" features a different character, and the sixth book rotates between all of them for the finale.
 * Phantasy Star III: Generations of Doom takes place over three generations, with a different protagonist and variations in the cast for each.

Web Comics

 * Recent story arcs of Rumors of War pair up characters for their day in the limelight. It makes for a veritable Cast-Go-Round, not unlike a Soap Wheel. The most recent (read: third) arc explored some of the consequences and repercussions of the very first story arc through the use of several Whole Episode Flashbacks (Chapters 13, 15, and 17).
 * Homestuck's Geodesic Cast has led to rotations within rotations: cast focus typically rotates between:
 * John
 * One of the other three Kids (which is in itself on a rotating basis: during Act 5-2, for instance, this has rotated from Jade to Dave to Rose).
 * Various Trolls
 * Other characters (rotating between the Exiles, the Guardians, Doc Scratch, the villains... and so on). Four Lines, All Waiting is a simplification of the situation. So do many MSPAFanVentures, which are in the same style as Homestuck. Examples are Be the Sea Dweller Lowblood and Adult Stuck.
 * Superego, itself an MSPA Fan Adenture, rotates between its ten characters and their experiences in a not-quite-normal hospital.
 * The Meek shifts its focus between the travelling Angora, the emperor Luca, and the rogue Soli.

Web Original

 * Land Games

Western Animation

 * Batman: The Brave and the Bold has an interesting variation on this trope, where Batman remains the protagonist nearly all of the time, each episode focuses on him teaming up with a different obscure character from the DCU. Though in some episodes (like "Aquaman's Outrageous Vacation!") even Batman himself gets pushed into the background.
 * Season 1 of X-Men: Evolution.
 * Justice League and, particularly, Unlimited are the kings of this trope, focusing on new previously-obscure DCU characters (both villains and heroes) in every episode. Although The Question does get a Character Focus, too, what with being the Ensemble Darkhorse.