Bad Girls is the seventh studio album by American singer-songwriter Donna Summer, released on April 25, 1979, by Casablanca Records. Originally issued as a double album, Bad Girls became the best-selling and most critically acclaimed album of Summer's career (before the release of On The Radio: Greatest Hits Volumes I & II). It was also her final studio album for Casablanca Records. In 2003, Universal Music re-issued Bad Girls as a digitally remastered and expanded deluxe edition.

Bad Girls reached the top of the US Billboard 200, where it stayed for six weeks: for one week on June 16, 1979 and then for five consecutive weeks from July 7 to August 4, 1979. Bad Girls also topped the Billboard R&B Albums chart for three weeks, from June 23 to July 7, 1979, and all cuts from the album topped the Disco Top 80 for seven weeks from May 26 to July 7, 1979. It contained the US Billboard Hot 100 number-one hits "Hot Stuff" and "Bad Girls", and the number-two hit "Dim All the Lights".

Summer became the first female artist to have two songs in the top three of the Billboard Hot 100 when during the week of June 30, 1979, "Hot Stuff" fell to number two and "Bad Girls" rose to number three.

Bad Girls was certified platinum — now double platinum — by the Recording Industry Association of America (RIAA) within a week of its release. At the 1980 Grammy Awards, Bad Girls was nominated for Album of the Year and Best Female Pop Vocal Performance and "Hot Stuff" won the first Best Female Rock Vocal Performance. Additionally, "Dim All the Lights" was nominated for Best Female R&B Vocal Performance and "Bad Girls" was nominated for Best Disco Recording.

Bad Girls is considered one of the greatest disco albums of all time. It was ranked by Rolling Stone's list of the Women Who Rock: The 50 Greatest Albums of All Time at number 23. The magazine wrote, "The late great Queen of Disco pulls out all the stops for an album that sums up Seventies radio, from ladies-choice smooch jams to filthy funk." In a BBC Music review of the album, Daryl Easla wrote, "Bad Girls is a fantastic reminder of when [Summer] was the Britney, Christina, Mary J and Missy of her day all rolled into one." Part of the song "Our Love", also available as a B-side, was copied by New Order on Blue Monday.

"I have a fantasy about rerecording that whole album," said singer Maria McKee. "It's fabulous."