Frontman Nicholas Petricca co-wrote this with singer/songwriter Nick Lerangis. The single is named after Professor Anna Sun at Ohio's Kenyon College, a well-liked and respected Sociology professor whose class the band members took while enrolled there. In a 2011 interview with Carson Daly on the talk show Last Call, Petricca was asked about the lyrics, and he explained "It's about college, about maintaining that bit of being a kid. Don't be afraid to play." >>

This song peaked at #10 on the US Billboard Alternative chart and #20 on the US Billboard Rock chart.

The Vampire Diaries TV series plugged this song on the season three premiere episode, "The Birthday."

Petricca told The Bay Bridged blog how this song is connected with the band's love of face paint: "It sort of originated from the 'Anna Sun' video. When we were brainstorming about the video, we wanted to have a sort of Peter Pan and the Lost Boys vibe to it. When we released that video in our home town we had a big party, and we brought face paint, just to emulate the vibe of the video and then it sort of organically became this ritual that we did at shows. People started coming to shows with face paint, we started bringing it and it became this tradition."