"Bad Girls" is a song by American singer-songwriter Donna Summer from her 1979 seventh studio album of the same name, released as the second single from the Bad Girls album on June 23, 1979, through Casablanca Records. The song was produced by Summer's regular collaborators Giorgio Moroder and Pete Bellotte, and co-written by Summer and the Brooklyn Dreams.

"Bad Girls" became a worldwide success, peaking within the top-ten in seven countries, including Spain and New Zealand. In the United States, it spent five weeks at number-one on the Billboard Hot 100 and sold over two million copies, simultaneously becoming, alongside "Hot Stuff", her most successful single. The single, which was the second-biggest song of 1979, also helped the Bad Girls album to reach the multi-platinum status in the US. Summer placed three songs in the Top 12 of the Billboard 1979 year-end charts.

The inspiration for Summer to write the song came after one of her assistants was offended by a police officer who thought she was a street prostitute. A rough version of the song had originally been written a couple of years before its release. Casablanca Records' founder Neil Bogart, upon hearing it, wanted Summer to give it to Cher for her upcoming album. Summer refused and put it away for a couple of years.

A 12" version of the song was released as a medley with "Hot Stuff". Although "Hot Stuff" was extended for the 12" version, "Bad Girls" remained in the four minutes, fifty-five seconds album version. A "Bad Girls" 12" version with a length of almost seven minutes was produced but never released commercially. A demo version of the song was released on the "deluxe edition" of Bad Girls.

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