"No Line on the Horizon" is a song by rock band U2; it is the opening and title track on their 2009 album No Line on the Horizon. An alternate version, "No Line on the Horizon 2", was included as a bonus track on some versions of the album. The song was developed during the band's earliest sessions in Fez, Morocco, and began with a drum beat by drummer Larry Mullen, Jr. The lyrics were inspired by a photograph of Lake Constance, titled Boden Sea. Many reviews of the song compared it to the band's other guitar-heavy songs, including "Elevation", "Vertigo", "Zoo Station", and "The Fly".

"No Line on the Horizon" was first developed the recording sessions in Fez, Morocco, and was recorded in one take. "No Line on the Horizon" stemmed from drummer Larry Mullen Jr. experimenting with several different drum beats; producer and co-writer Brian Eno sampled and manipulated the patterns, and the rest of the band began to play over it. The guitar in "No Line on the Horizon" was developed through a Death by Audio distortion box; the idea to use it was suggested to guitarist the Edge by Ben Curtis of the Secret Machines. After hearing the song Curtis noted that it "blew my mind... he's using that pedal in a textural way that it wasn't intended to be used at all."

Lead singer Bono was inspired to write the lyrics after seeing a photograph of Lake Constance titled Boden Sea; the image had taken by Japanese photographer Hiroshi Sugimoto. Bono had the idea of a place "where the sea meets the sky and you can't tell the difference between the two". When it came to recording the song, producer and co-writer Daniel Lanois stated that "the vocal happened very early on, that whole - a-whoawhoawhoawhoa! - that little hook. The vocal delivery, the vibe was there right from day one." Bono noted that the overlying theme behind the song was infinity, and that the track was inherently optimistic. The Boden Sea image would later become the album's cover art.

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