Step 1 : Introduction to the question "Which song is the biggest-selling sheet music in rock history?"
...Not only is Led Zeppelin's "Stairway to Heaven" at the top of the all-time rock favorites list, it sits atop the list of most sheet music ever sold. "Stairway to Heaven" sheet music proudly boasts it's sold one million copies. The iconic rock band Led Zeppelin performed "Stairway to Heaven" in just about every concert they did. The song continues to get air time over 4,000 times per year, according to "Monday Morning Replay" trade magazine. It is a popular favorite on America's album-oriented rock (AOR) radio stations. Source: ClassicRockWorld.org