"LDN" (shorthand for, and pronounced as, "London") is a song by English recording artist Lily Allen. It was co-written by Future Cut, and features a Colombian porro from the country's Caribbean coast. The song was originally released on strictly limited edition 7" vinyl (500 copies) in the UK on 24 April 2006, accompanied by album track "Knock 'Em Out", and was re-released in September following the huge success of Allen's first mainstream single "Smile".

The re-release peaked at number six on the UK Singles Chart. The song is used in the soundtrack of the film The Nanny Diaries, and in the trailer for Happy-Go-Lucky. This song was number 30 on Rolling Stone's list of the 100 Best Songs of 2007. In 2008 the song was included in the soundtrack of the Mike Leigh film Happy-Go-Lucky. Allen claims that the inspiration for the song was William Wordsworth's poem "Composed upon Westminster Bridge, September 3, 1802".

Regal Records gave Allen £25,000 in 2005, when she signed to the label, a fact which she considered to be a "small development idea". The money was to produce an album, though they were unable to provide much support for it due to their preoccupation with other releases. Taking advice from Lady Sovereign, Allen created an account on MySpace and began posting demos in November 2005. By March 2006, they attracted thousands of listeners, and 500 limited edition 7" vinyl singles of one of the demos, a song titled "LDN", were rush-released and sold for as much as £40, thus the song becoming her first actual single.

Allen also produced two mixtapes to promote her work. As she accumulated tens of thousands of MySpace friends, The Observer Music Monthly took interest. Few people outside of her label's A&R department had heard of Allen, so the label was slow in responding to publications who wanted to report about her. Her label wasn't pleased with the sound of the demos, so they assigned the singer to top producers and songwriters, and after they finally approved some of her songs, confident on the inclusion on the album. Among the songs that Allen claimed she was happy with was "LDN".

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