"Lost Without You" is a pop ballad written by Bridget Benenate and Matthew Gerrard, produced by Gerrard for Delta Goodrem's first album Innocent Eyes (2003). It was released as the album's second single on 28 February 2003 (see 2003 in music) in Australia and in the middle of 2003 for the rest of the world. The song became Goodrem's second number-one single in Australia and also peaked in the top ten in New Zealand, the UK and Sweden. Goodrem re-mixed and recorded the song for the United States and the song was released there on 28 June 2005 (see 2005 in music) as a digital download.

"Lost Without You" was released to Australian radio early February 2003 and was the most added song to radio for that week. The song debuted on the Australian ARIA Singles Chart on 10 March 2003 at number-one knocking "Beautiful" by Christina Aguilera off the top spot. It was certified gold in its first week by ARIA and it became Goodrem's second consecutive number-one single. On its second week in the charts, it was knocked off the number-one spot by "All the Things She Said" by t.A.T.u., but then in its third week it re-gained the number-one spot spending a total of two weeks at the peak. It was then knocked off the top again by "All the Things She Said". "Lost Without You" spent twelve weeks in the top ten, eighteen weeks in the top fifty, thirty-two weeks in the top one hundred, was certified double platinum by ARIA and was the seventh highest selling single in Australia for 2003. The song debuted at number thirty-one on the New Zealand RIANZ Singles Chart on 29 June 2003. It took eleven weeks to get to its peak position of four and it spent nineteen weeks in the charts.

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