 Musical works in the Western classical tradition admit of multiple instances (performances). Much of the debate over the nature of such works thus reads like a recapitulation of the debate over the “problem of universals”; the range of proposed candidates covers the spectrum of fundamental ontological theories. We might divide musical ontologists into the realists, who posit the existence of musical works, and the anti-realists, who deny their existence. Realism has been more popular than anti-realism, but there have been many conflicting realist views. I begin with three unorthodox realist views before moving on to more orthodox Platonist and nominalist theories, concluding with a consideration of anti-realism.