Along with twentieth-century developments in playing techniques, technologies, and concepts of musical sound, the notations employed by composers have also changed. Composers of what Umberto Eco calls 'open works' often employ intentionally ambiguous music notations. These open notations ask the performer to play a radical and active role in co-creating the musical work. Scores that feature open notations have been part of the Western classical music landscape since the mid-twentieth century, and continue to have a vibrant community of practitioners today. In this Element, Tristan McKay considers intersections of ambiguity, authority, and identity in works with open notations. He develops a semiotic approach to open notation analysis and puts it into practice with in-depth analyses of openly notated works by Earle Brown, Will Redman, and Leah Asher.