Vague expressions, such as "heap," "red" and "child," proliferate throughout natural languages, and an increasing amount of philosophical attention is being directed at theories of the logic and semantics associated with them. In this book Rosanna Keefe explores the questions of what we should want from theories of vagueness and how we should compare them. Her powerful and original study will be of interest to readers in philosophy of language and of mind, philosophical logic, epistemology and metaphysics.