This article addresses the long-standing problem of how to understand Mill’s famous harm principle in light of his failure to specify what counts as “harm” in On Liberty. I argue that standard accounts restricting “harm” to only certain negative consequences fail to do justice to the text, and that this fact forces us to rethink Mill’s defense of individual liberty. I then offer a new account of that defense in which “harm” is understood in an expansive sense, despite apparent problems for such a view.