­Comedian Jerry Seinfeld's self-titled show mastered the successful sitcom formula.

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Sitcom Format

A sitcom typically lasts around 30 minutes. In the early days of television, the show's advertising came before the opening credits and at the end credits, using only about two and a half minutes of the show's 15 or 30 minutes. Frequent advertising breaks cut today's half hour programs down to 22 minutes.

A sitcom usually has four main characters. In most cases, they include a hero, an anti-hero, a love interest and a buddy. Of course, there are always variations of this theme, but it's a common formula. Even a seemingly unlikely example like the family sitcom "Married with Children" fits the type. Ed is the unlikely hero, Peg, the anti-hero, Kelly, every high school boy's love interest and Bud, well, the buddy.

Since sitcoms are only 30 minutes long, it is essential that the plot line be fairly tight and resolvable. Successful plots will typically fall within a family or workplace setting or some combination of the two. Within this setting, there are A and B storylines. An A storyline is the main plot of the sitcom. In most cases, the A story runs throughout the show and does not resolve until the final scene. The B storyline is secondary. Depending on how many characters are in the cast, there can be other peripheral stories -- C, D, and so on. Throw in a hook or plot twist and you have a show.

Sitcoms also often have teasers -- a short scene that appears before or during the opening credits. Not all shows have them, but most include them as a way to get the audience laughing as they click through channels. The teaser may or may not directly relate to the A or B storyline. One example of a great teaser can be seen in the early episodes of "Seinfeld." Jerry Seinfeld uses a short stand-up routine to set the audience up for what they were going to see. His teaser is a lead-in joke or humorous observation.

The key to a successful sitcom is variety and character-driven humor like the running gag or inside joke. The running gag is a funny situation or line of dialogue that reappears in an episode or series of episodes. Sometimes the running gag becomes a catchphrase. The line or situation is often unintentional at first, but ends up striking a chord with the audience. When the audience reacts favorably, the line or the situation gets written back in and usually becomes funnier because of its multiple appearances. The success of the running gag or inside joke relies on the actor's delivery.

In the next section, we'll learn how the sitcom on paper translates to the show on the small screen.