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
* AnimeThemeSong (Opening Theme)
* BootstrappedTheme
* BraggingThemeTune
* CyberPunkIsTechno
* DoItYourselfThemeTune
* EndingTheme
* ExpositoryThemeTune
* ForeignLanguageTheme
* InstrumentalThemeTune
* LastEpisodeThemeReprise
* NationalAnthem
* NoThemeTune
* RealSongThemeTune
* RearrangeTheSong
* ReplacedTheThemeTune
* SolemnEndingTheme
* SurrealThemeTune
* ThematicThemeTune
* ThemeTuneCameo
* ThemeTuneExtended
* ThemeTuneRap
* ThemeTuneRollCall
* TitleThemeDrop
* TitleThemeTune
* TranslatedCoverVersion
* TruncatedThemeTune
* VariationsOnAThemeSong
* WhatSongWasThisAgain