"Nightswimming" is a song by the American alternative rock band R.E.M. It was released in 1993 as the fifth single from the group's eighth album Automatic for the People (1992). "Nightswimming" is a ballad featuring singer Michael Stipe accompanied only by bassist Mike Mills on piano (lyrics and music respectively, but credited to the whole band as usual), a string arrangement by former Led Zeppelin bassist John Paul Jones, and a prominent oboe by Deborah Workman in the latter part of the piece. Stipe sings about a group of friends who go skinny dipping at night, which draws from similar experiences in the band's early days.

Bassist Mike Mills recalled he was playing a piano riff at John Keane's studio in the band's hometown of Athens, Georgia. While Mills almost discarded the melody, it attracted the interest of singer Michael Stipe. Mills said, "I never thought it would amount to much because it was just a circular thing that kept going round and round and round. But it inspired Michael." While the song was not included on Out of Time, the demo recorded during those sessions was used for Automatic for the People, with a string arrangement by John Paul Jones added to the track. Mills has also claimed he recorded the piano part at Criteria Studios in Miami, on the same piano used by Derek and the Dominos on the recording of "Layla".

"Nightswimming" was performed solely by Michael Stipe and Mike Mills; Stipe sings while Mills plays the piano. R.E.M. guitarist Peter Buck noted that the absence of drummer Bill Berry and himself from the song was typical of many tracks on Automatic for the People, where one or more bandmembers would not appear on a given song. Mills plays a piano motif he has referred to as "circular" in nature.

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