Under the Iron Sea is the second studio album by English rock band Keane, released in 2006. During its first week on sale in the UK, the album went to #1, selling 222,297 copies according to figures from the Official Chart Company. In the United States, the album came in at #4 on the Billboard 200, selling 75,000 units in its first week. Since January 22, 2006, the album had sold above 3,000,000 copies worldwide.
The band describes Under the Iron Sea as a progression from Hopes and Fears with electronic influences, describing the record as a "sinister fairytale-world-gone-wrong".
After the release of their debut album, Hopes and Fears, Keane embarked upon a world tour that reached virtually all Europe and North America and which culminated on October 2005. As seen on Strangers, the band had been having trouble since the middle of 2004, shortly after the release of the debut. The suggestion "Hamburg Song" is about the bad-turned relationship between singer Tom Chaplin and pianist Tim Rice-Oxley - composed circa August 2004 - develops the focus of the conflict. During the tour, Rice-Oxley kept composing new songs that would later appear in future releases such as B-sides "Let It Slide" and "Thin Air". According to Chaplin, Rice-Oxley had composed at least 50 new tracks as of April 2006.
The name of the album is based on a lyric appearing on the track, "Crystal Ball" which reads "I've lost my heart, I buried it too deep, under the Iron Sea". It also shares title with the eighth track and Keane's first instrumental, "The Iron Sea". The "Iron Sea" is the metaphoric name for the group's (especially Rice-Oxley's) preoccupations about their uncertain future and the sudden fame they were having.