• Acting for Two: Jerry Stiller as Frank Costanza, and the implied relative Giuseppe in "The Doll", poorly disguised by Seinfeld standards, even compared to Jerry Seinfeld and Jason Alexander playing their characters in high school in "The Library".
  • Actor Allusion: In the JFK parody in "The Boyfriend," Newman replicates his position standing in front of Kramer, just as Wayne Knight did in the movie standing in for John Connally in the courtroom demonstration of the "magic bullet" theory.
    • A picture of a dinosaur appears in Newman's apartment, referencing Knight's role in Jurassic Park.
  • The Danza: Jerry Seinfeld's character is named... "Jerry Seinfeld".
    • George's mother Estelle is named after her actress. But they couldn't name his father the same way because they already had a Jerry.
    • But, George's dad was originally played by John Randolph.
    • In "The Kiss Hello", Wendie Malick as Wendie the delicate genius.
  • Descended Creator: As the show went on, Larry David had more and more Creator Cameos usually seen only from behind or voicing unseen characters like George Steinbrenner, a part David continued to voice for some time after he had already left the series as a writer.
  • Directed by Cast Member: Jason Alexander directed Season 3's "The Good Samaritan".
  • Dueling Shows: With Everybody Loves Raymond.
  • Edited for Syndication: Most episodes feature little dialog cuts here and there to save time for more commercials.
    • The episode which suffers the worst in this regard is "The Yada Yada", as it originally ran 26 minutes in its NBC premiere.
    • Since 2010, most markets air the episodes in a cropped format (similar to a x1.2 zoom on most DVD players), and as such, all on-screen titles (opening credits, closing credits, subtitles, etc) have been changed accordingly. Some episodes also have either repositioned the show logo in the opening, or left alone, resulting in half of the 'S' in Seinfeld being cut off.
    • The pilot episode had an entirely different theme song, the on-screen title was The Seinfeld Chronicles, the credit titles were in a different font, and the end titles played over a plain black screen. In syndication, however, the original theme is replaced with Jonathan Wolff's theme, The Seinfeld Chronicles title is replaced with Seinfeld, the titles are in the tradition Movie Poster font like the rest of the series, and the end titles are plastered over still shots of Jerry's standup riffs.
  • Fake Brit: Norman Brenner's character in "The Wig Master".
    • Subverted. Brenner is actually British.
  • Hey, It's That Guy!: Hey, it's Monica, Janice, Susan, Daphne, Kitty, Robert, and even a youthful Dr. Cuddy!
  • Hey, It's That Voice!: J. Peterman's actor can unmistakably be heard as the voiceover in current Coors Light commercials.
  • I Am Not Spock: It's happened to pretty much every cast member except Jerry Seinfeld. Particularly Wayne Knight. On one instance, after a bad day, he snapped at someone who greeted him with "Hello, Newman...". On the other hand, Jason Alexander once appeared on Real Time with Bill Maher, and one of his fellow panelists agreed with him by saying "You know, George is right..." Cue a big "OOOOOOOH" from the audience. Alexander, however, laughed it off with a good-sported remark that "Hey, I'm still getting the royalty checks."
    • Alexander also got into a bit of quote call-backs during some hands at the 2010 World Series of Poker, and once mentioned he was grateful for George Constanza, because he'd otherwise be known as the guy who tried to rape Julia Roberts.
    • During the Laugh Factory incident, various media outlets kept referring to Michael Richards as Kramer, to the point that the real Kramer, Kenny Kramer, issued a statement saying that he personally was not a racist.
    • And all four cast members reunited for an episode of Curb Your Enthusiasm.
      • Speaking of Curb, even earlier than that, in Season 2, a plotline revolved around Larry trying to get a show off the ground about an actor who can not escape their previous popular sitcom role, first with Jason Alexander and then with Julia Louis-Dreyfus.
  • Missing Episode: "The Puerto Rican Day" has a scene where Kramer (accidentally) burns a Puerto Rican flag. Many viewers were highly offended, and NBC decided to leave the episode out of syndication for several years. Although it does occasionally air on local stations today, many stations still skip it (including TBS) and those that don't often cut out the flag-burning scene. You can see it uncut on DVD, though.
    • For a time, "The Invitations" was removed from syndication because Susan dropping dead from licking toxic envelopes reminded people of the anthrax mail scares. It returned to rotation in summer 2002.
  • Old Shame: Regis Philbin loves the series, so he was disappointed that when he guest starred, he was given a line that he didn't think was funny (three variants of "This guy's bonkos!"). The producers insisted it would be hilarious, but his lines didn't get very many laughs with the studio audience. To this day, Regis dreads watching that episode for that reason.
  • The Other Darrin: Phil Bruns originally played Morty Seinfeld, but after his initial appearance, he was played by Barney Martin.
    • Larry David originally played Newman in "The Revenge" (he provided his off-screen voice), but his first on-screen appearance was by Wayne Knight. In syndication, Knight dubbed over David's voice in "The Revenge" to provide some continuity. However, both versions of the episode are available on the DVD set.
    • John Randolph originally played Frank Costanza in "The Handicap Spot". Later, Jerry Stiller replaced him in "The Puffy Shirt". For syndication, John Randolph's scenes in "The Handicap Spot" were re-shot with Jerry Stiller in his place, to provide continuity. However, as with the previous example, both versions are available on DVD. One weird effect of this is that George says his father is bald in an earlier episode, which fit Randolph but not Stiller.
    • Lloyd Braun was initially played by Peter Keleghan, and later played by Matt McCoy in "The Gum" and "The Serenity Now".
  • The Other Marty: See The Other Darrin above for details.
  • What Could Have Been: Larry Miller was originally cast as George, but it was decided that, just to make George a little bit more pathetic, he needed to be short. Miller eventually appeared as a doorman that could give The Janitor a run for his money.
    • The project began as just a 90 minute special about a day in Jerry's life, and how it inspires his stand-up material that night. Jerry and Larry David couldn't quite stretch the script to fill the 90 minutes, so they reduced in down to half an hour as a series pilot. As Jerry would later say, "We couldn't make 90 minutes, so we made 90 hours."
    • Elaine's father was intended to be a recurring character, but then they hired the notoriously ill-tempered and intimidating Laurence Tierney to play him, and after filming the episode, no one wanted to work with him again.