"I Don't Know What It Is" is a song written and performed by Canadian-American singer-songwriter Rufus Wainwright. It was the first single from Wainwright's third studio album Want One and was released in a slim-line jewel case format on July 26, 2004. In addition to the UK and Japanese versions of Want One, the song also appears on the bonus DVD that accompanies Want Two (Rufus Wainwright: Live at the Fillmore), All I Want (DVD), and Want, a repackaged UK double album that contains Want One and Want Two.