"Whatsername" is the 13th track of the Green Day album American Idiot. Whatsername is also a character from the same album's plot. The song has a key signature of D, and is played in drop D tuning, the only Green Day song so far to use this tuning.

The chord progression and rhythm are somewhat similar to the 1996 song "One Headlight" by the Wallflowers.

Whatsername is the main love interest of the character Jesus of Suburbia. Interestingly, Jesus of Suburbia either never knew her name, or could never remember it (as referenced in the track "Whatsername"). He meets her on July the 4th, and details this in "She's a Rebel".

In the next song, "Extraordinary Girl", she goes out with him, but they start to drift apart, possibly because Whatsername doesn't like that Jesus is now St. Jimmy.

In Letterbomb, Whatsername sends Jimmy a letter. According to Jimmy, Jesus' alter ego, "she said 'I can't take this place, I'm leaving it behind.' She said, 'I can't take this town, I'm leaving you tonight.'"

In "Homecoming", JoS destroys his Saint Jimmy persona and returns to Jingletown.

Whatsername is a rebel, and the "missing link on the brink of destruction." In the track "Whatsername", Jesus of Suburbia mourns her leaving him. In this song, there appears to be a play on words. Jesus can't remember Whatsername's name, so he calls her Whatsername, as shown "I remember the face but I can't recall the name, now I wonder how Whatsername has been..." It should also be noted that throughout the album's lyric booklet a name is scratched out and replaced by "Whatsername", which implies that he's been trying to forget about her all these years.

Although Jimmy is clearly sad that she is gone he displays a certain anger at, or at least an attempt to forget, her, as shown in "I made a point to burn all of the photographs." He also has a somewhat detached feeling from her as though he used to care but now has given up all hope, "did she ever marry old Whatshisface" as though it is a matter of small interest.

Jimmy accepts that they have gone their separate ways, claiming that he will never "turn back time," and will "forget [her] but not the times."