"Theme to St. Trinian's", also known as "Defenders of Anarchy", is a promotional single recorded by British all-female pop group Girls Aloud for the album St. Trinian's: The Soundtrack (2007), released to promote the film of the same name. The song was written by the film's score composer Charlie Mole and Ali Thompson, while Girls Aloud's recurring collaborators Xenomania provided production.

The track was recorded by Girls Aloud to coincide with their cameo appearance in the film as the St. Trinian's School Band. A music video of their performance from the film was used to promote the track, which was available for digital download alongside the rest of the soundtrack album on 10 December 2007. "Theme to St. Trinian's" charted at number 51 before being removed by Fascination Records to avoid confusion with Girls Aloud's actual single "Call the Shots".

The song was written specifically to serve as the theme tune to the 2007 film St. Trinian's. It was written especially by the film's composer Charlie Mole, with additional lyrics by Ali Thompson. The song was offered to many artists, but was eventually given to Girls Aloud and produced by their production team Xenomania. It was revealed in April 2007 that the band would make a cameo appearance in the film as the St. Trinian's School Band, when they were photographed in school uniforms on the movie's set. It was later announced that aside from appearing in the film, the group would be recording the main theme for the soundtrack. "Theme to St. Trinian's" was later re-recorded by the Banned of St. Trinian's under the title "Defenders of Anarchy"; this appeared on the soundtrack to St Trinian's 2: The Legend of Fritton's Gold and was also produced by Xenomania. Coincidentally, Girls Aloud member Sarah Harding had a starring role in the film.

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