"One Week" is a 1998 hit single by Barenaked Ladies. It is often regarded as the song that propelled the band to superstar status outside Canada. One reason for the song's popularity was the large number of pop culture references worked into the lyrics. It remains the band's biggest hit to date.

The song gained renewed popularity when it was featured in an ad for the Mitsubishi Lancer, with groups of young people in the car seeming to sing along until they could not keep up with the rapid-fire lyrics. It was featured in the third installment of Big Shiny Tunes.

Ed Robertson wrote the ideas for the non-rap 'choruses' with the concept being the structure of a fight where the protagonist knows they are wrong and is just trying to save face. He wanted to come up with a rapping verse for the song but all attempts failed. Bandmate Steven Page suggested he simply improvise the rap as the two commonly did onstage every night. Robertson heeded the advice and set up a video camera. He improved the song at a slower pace to make rhyming easier and arrived at about four minutes of rap. He sent it to Page who told him not to change a word. Two minutes of the improvising was almost directly compiled (with very little, if any, tweaking) into the verses of the song. As it is improvised, it is not intended to directly have any relation to the plot of the chorus sections. The liner notes from Stunt contain some of the additional lyrics that did not make it into the recorded version.

In recent performances, the band has developed an acoustic, bluegrass version of the song. It is used in a new performance setting they developed in 2003, in which they play acoustically while they stand around and sing into one omni-directional microphone.

Although the song topped the U.S. Hot 100, it peaked at number nine on the Canadian Singles Chart partly because of limited promotion. It also topped the Modern Rock Tracks for four non-consecutive weeks.