This is the first detailed study to explore the little-understood notions of "knowing who someone is," "knowing a person's identity," and related locutions. It locates these notions within the context of a general theory of believing and a semantical theory of belief- and knowledge-ascriptions. The books's main contention is that what one knows, when one knows who someone is, is not normally an identity in the numerical sense of "a = b," but rather...