The piece of music which plays over the opening and/or closing credits of a UsefulNotes/{{Television}} show, and is intended to become intimately identified with the series.

Theme tunes began in the earliest days of {{radio}}, where there were no specific {{networks}} to switch to and listeners would often have to tune their crystal sets with some precision in order to pick up the correct station, which may have been located hundreds of miles away. A theme tune allowed them to select the correct station. Shortwave radio stations still use theme tunes, called ''interval signals'', at the beginning of their transmissions. Well-known interval signals include the Voice of America's ''Yankee Doodle'' and the BBC World Service's ''Lilliburlero''.

Theme songs are usually original works, but some shows use a song that has already been recorded (see RealSongThemeTune).
A theme song may be an instrumental or have lyrics, although most dramatic shows (including, as far as America is concerned, those animated) use an InstrumentalThemeTune.

SitCom theme song lyrics have gone through various phases. Radio theme songs were generally [[InstrumentalThemeTune instrumental]], possibly because it was hard to hear lyrics over music on old low-fidelity radio sets. Sitcoms that moved to television kept their old instrumental tunes, while new sitcoms created for television could choose an instrumental tune or an ExpositoryThemeTune. From the mid-1970s to the mid-1990s most sitcoms featured a ThematicThemeTune. The current trend is toward the SurrealThemeTune or NoThemeTune whatsoever. It's also possible for theme tunes to [[ReplacedTheThemeTune be replaced]].

See {{Leitmotif}} for character themes or music for recurring events. For ''other'' themes see CentralTheme.

For further listening, [[]] has a ''huge'' library of various theme songs and other musical numbers.
!!Theme Tune subcategories include:
* AlternativeForeignThemeSong: When a TV show is dubbed, the theme song is replaced with a different one.
* AnimeThemeSong: A jaunty pop-type song that's the theme tune to an anime cartoon.
* BootstrappedTheme: When a theme that was formerly only associated with one character/setting/whatever becomes extremely popular, which leads to it getting heavily associated with the work and then it becomes the main theme tune.
* BraggingThemeTune: The theme tune boasts about how amazing a character is.
* CyberPunkIsTechno: Techno theme music is used for a technologically-advanced, dystopian future setting.
* DoItYourselfThemeTune: The theme song is written/sung by one or more characters (but not necessarily within an episode).
* EndingTheme: A certain tune that plays at the end of all or most episodes.
* ExpositoryThemeTune: The theme tune explains the premise of the show.
* ForeignLanguageTheme: The theme tune is in a different language than the rest of the show.
* InstrumentalThemeTune: The theme tune has no lyrics, just music.
* LastEpisodeThemeReprise: The theme tune gets played in the score of the climax of the last episode.
* NationalAnthem: The theme song of a whole country.
* NoThemeTune: The show [[AvertedTrope doesn't have]] a theme tune.
* OpeningNarration: A short voice-over at the beginning of every episode, explaining the show's premise.
* RealSongThemeTune: The theme tune was already a song before the show was made.
* RearrangeTheSong: Rewriting the theme tune.
* ReplacedTheThemeTune: Similar to Rearrange the Song, but replacing the theme tune with an entirely different song.
* SignatureSong: The creator's most famous song, not always a theme tune but often is.
* SolemnEndingTheme: An Ending Theme that sounds wistful.
* SurrealThemeTune: A theme tune with surreal, nonsensical and often irrelevant lyrics.
* ThematicThemeTune: A theme tune where the premise is similar to the show's premise but is not an Expository Theme Tune.
* ThemeTuneCameo: The theme tune is sung/played/hummed/whistled/etc in an episode.
* ThemeTuneExtended: The show's writers make a longer version of the theme tune.
* ThemeTuneRap: The theme tune is a rap.
* ThemeTuneRollCall: The theme tune lists the characters.
* TitleThemeDrop: The theme tune is in the score.
* TitleThemeTune: The title of the show is said within the theme tune.
* TranslatedCoverVersion: Dubs of the theme tune.
* TruncatedThemeTune: The theme tune gets cut down to one verse, usually for profit.
* VariationsOnAThemeSong: The theme tune gets changed up for an episode.
* WhatSongWasThisAgain: The dubbed song has extremely different lyrics than the original.