"Sunday Girl" was written solely by Blondie guitarist Chris Stein. Stein recalled, "I wrote that one all by myself, but I was so nervous about having my own song, I asked [Debbie Harry] to put her name on it. ... We left [the credit] to me in the long run."
The song "Sunday Girl" was written solely by Chris Stein, but Blondie's lead singer, Debbie Harry, contributed to its creation through a collaborative process.