Written by Chris Stein to cheer up Debbie Harry after her cat went missing, "Sunday Girl" is a quintessential pop-rock hit from Blondie's Parallel Lines era that blended new wave edge with a catchy, melancholic sound. While it achieved major success as a UK #1 single in 1979, the track was notably not released as a single in the United States, and also featured a special French-language version.