The book is about the problem of vagueness. It begins by discussing some of the existing views on vagueness and then explains why they have not been thought to be satisfactory. It then outlines a new account of vagueness, based on the general idea that vagueness is a global rather than a local phenomenon. In other words, the vagueness of an expression or object is not an intrinsic feature of the object or an expression but a matter of how it relates to other objects and expression. The development of this idea leads to a new semantics and logic for vagueness. The semantics and logic are then applied to a number of issues, including the sorites paradox, the transparency or luminosity of mental states, and personal identity. It is shown that the view allows one to hew to a much more intuitive position on these various issues.