"A Bad Dream", often mistitled as "Bad Dream", is a song by English piano rock band Keane appearing as the fifth track on their second album, Under the Iron Sea. It was released on 22 January, 2007 as the sixth and final single from the album. The song peaked at #23 in the UK Singles Chart, becoming the band's first single to miss the top 20.

A track titled "The Night Sky" was believed to be the obvious choice for a B-side as it was an unreleased track on Under the Iron Sea, mentioned several times and thought to have a relation with the song, but Keane instead included for the first time both cover songs ("She Sells Sanctuary" by The Cult and "Enjoy the Silence" by Depeche Mode) and a remix of the single by the noted hardcore artist Luna-C in the commercial release. "The Night Sky" was instead released as the next single.

Catalogue number: 1723057

Catalogue: 1723058

It was composed by Tim Rice-Oxley and Tom Chaplin. It was recorded at the Heliocentric Studios, Rye, East Sussex and at The Magic Shop, New York.

It was partially based on the "An Irish Airman Foresees His Death" poem by W.B. Yeats. Rice-Oxley explained on a podcast:

This song is a cover of The Cult's original song. It's the first song released since June 2001 ("She Has No Time") that includes acoustic guitar on the recording.

The song includes a hardcore style instrumentation never heard on a Keane release before.

The music video for "A Bad Dream" was shot on 22 November 2006 and premiered a month later. The essentially simple promo features singer Tom Chaplin walking through white and dark lights.

An alternate version released on Yahoo Launch UK features short clips of Tim Rice-Oxley and Richard Hughes intercut into the original, looking at Chaplin with melancholic faces.