"You Lost Me" is a song by American recording artist Christina Aguilera, taken from her fourth studio album, Bionic (2010). Described by Aguilera as the "heart of the album", it was co-written by Aguilera, Sia Furler and the producer of the song, Samuel Dixon. Lyrically, the song talks about a cheating man, who has left her world "infected". The song was released on June 27, 2010 by RCA Records, as the third US single and second international single from Bionic.
"You Lost Me" was well received by contemporary critics, who noted it as one of the album's highlights and complimented the song for being a return to Aguilera to the time before its preceding single, "Not Myself Tonight", was released. Commercially, the song failed to make an impact, becoming her first US single to fail to enter the US Billboard Hot 100, although it was successful on the Hot Dance Club Play chart, where it reached number one. Internationally, it had the same chart performance, peaking within the top-twenty in Belgium and Israel.