"Bad Blood" is a song by American singer-songwriter Taylor Swift, from her fifth studio album 1989 (2014). The remixed version of the song, featuring American rapper Kendrick Lamar, was released on May 17, 2015, by Republic Records as 1989's fourth single. The album version was written by Swift, Max Martin, and Shellback, with Lamar writing his verses on the remixed version. The lyrics of "Bad Blood" describe the betrayal of a close friend. The album version is the eighth track of 1989.

The song reached number one in Australia, Canada, Israel, New Zealand, Scotland, and the United States, becoming the third song from 1989 to do so. The accompanying music video was directed by Joseph Kahn and features an ensemble cast. The video previously held the 24-Hour Vevo Record with 20.1 million views, before being surpassed by Adele's "Hello". It won Video of the Year and Best Collaboration at the 2015 MTV Video Music Awards. The song received a nomination for Best Pop Duo/Group Performance while its music video won Best Music Video at the 58th Grammy Awards.

A cover version of "Bad Blood" was released as the first promotional single from singer-songwriter Ryan Adams' interpretation of Swift's 1989 album, released in September 2015.

"That was about losing a friend… But then people cryptically tweet about what you meant. I never said anything that would point a finger in the specific direction of one specific person, and I can sleep at night knowing that. I knew the song would be assigned to a person, and the easiest mark was someone who I didn't want to be labeled with this song. It was not a song about heartbreak. It was about the loss of friendship."

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