Patrick Leonard, who wrote and produced many of Madonna's hits, wrote this song. He explained in 1000 UK #1 Hits
by Jon Kutner and Spencer Leigh: "Madonna rang me up one night and told me she wanted an uptempo song and a downtempo song. She came over one night. I had already put down the chorus for a song on a cassette, she took it into the back room, while I worked on the rest of the lyrics. Soon after, she came out and said, 'We'll call it 'Who's That Girl.'' The backing track was recorded in one take and Patrick Leonard added the guitars and percussion the next day."