This chapter develops an account of modal structure. Modal structure is the way in which various basic elements of reality, say properties and particularities, involve modality, which is to say possibility and necessity, in their essence. The specific form of modal structure involved in the cases this book considers is that of “the superworld.” It involves a local entwining in being of the merely possible and the actual. For instance, a specific shade of scarlet is entwined in being with the real possibility of other specific hues to which it bears essential relations of similarity. This view of the truth grounds of certain modal claims is motivated by a critical examination of extant views. For instance, there is a revealing analogy between time and modality, which undercuts standing views of mere possibilia. Presentism, the view that facts about the past are constituted by various facts now, can be legitimately accused of changing the subject, of not really providing an account of what is truly past, but rather talking about something else. So too standing views of possibilia. Possibilism, which identifies possibilities with existing things spatially disconnected to us, and actualism, which identifies possible concrete objects with various existing abstracta, also improperly change the subject, and so fail as accounts of what is truly merely possible. Rather, a genuinely different type of being is possessed by certain possibilia, which I call mere “subsistence.” This is a variation of some classical metaphysical views, for instance Aristotle’s notion of focal being.