A World to Believe In (Japanese: あなたがいる限り^?, Hepburn: Anata ga Iru Kagiri, "As Long as You are with Me") is the second single released in Japan from Celine Dion's 2007 album Taking Chances. It was also the first and only single for the new Japanese greatest hits album, Complete Best (2008). The song, originally performed in English by Dion only for Taking Chances, was re-recorded as a duet with the Japanese singer Yuna Ito, and released as a CD single on 16 January 2008.

"A World to Believe In" was written by Tino Izzo and Rosanna Ciciola, and produced by Grammy Award-winner John Shanks.

The track was re-recorded in October 2007 as an English-Japanese duet with Yuna Ito, retitled as "あなたがいる限り: A World to Believe In." Dion was impressed when she heard Ito's cover of "My Heart Will Go On", featured on the Japan only released tribute album Tribute to Céline Dion from 26 September 2007, and proposed the idea of the duet together. The song was also featured on Ito's album, Wish.

"A World to Believe In" follows Ikimono-gakari's "Akaneiro no Yakusoku" to become the ninth LISMO cellphone service TV commercial song, aired from 1 December 2007.

The single debuted at number eight on the Japanese Oricon Singles Chart with 11,778 copies sold. In its second week it dropped to number twenty-two with 5,399 copies. After eight weeks the single has sold 24,105 copies in total. On the Oricon Daily Singles Chart the song peaked at number six.

"あなたがいる限り: A World to Believe In" (U.S.A. mix) subsequently appeared as the first track on Dion's greatest hits album, called Complete Best, released on 27 February 2008.

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