"In Cold Blood" is a song by British indie rock band alt-J. It is the second track and second single from their third studio album, Relaxer, and was released as a digital single on 29 March 2017 by Infectious Music and Atlantic Records. The song was written by Joe Newman, Gus Unger-Hamilton, and Thom Sonny Green and produced by Charlie Andrew. It features a brass section recorded at Abbey Road Studios in London and a Casiotone the band purchased for £1.05 on eBay. The song's title is a reference to the novel of the same name by American novelist Truman Capote. The song's composition dates back to when the band started during their studies at the University of Leeds.

In an interview with NPR, the band said:

The music video for the song was released on 9 May 2017. It was directed by Casper Balslev, who had previously directed videos for Marina and the Diamonds and MØ. The video is narrated by Iggy Pop, frontman of The Stooges.

On 18 April 2017, alt-J performed "In Cold Blood" on the 656th episode of The Tonight Show Starring Jimmy Fallon. The band performed the song with a backing horn section and with Questlove, the drummer of Jimmy Fallon's house band The Roots. On 19 May 2017, alt-J performed "In Cold Blood" on the sixth episode of the fiftieth series of Later... with Jools Holland. On 5 June 2017, alt-J performed "In Cold Blood" on Conan.

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