This chapter combines recent work on vagueness in the philosophy of language with recent work in the philosophy of law on the value of vagueness in certain legal situations. The question at issue is whether leading philosophical theories of what vagueness is can account for the positive utility of certain kinds of legal vagueness. The two theories put to the test are (i) epistemicism, according to which vagueness is a matter of irremediable ignorance of the sharp borderlines separating cases in which (totally defined) vague predicates apply from those in which their negations do; and (ii) the theory according to which vague predicates are (a) only partially defined, leaving a range of borderline cases in which there is no fact of the matter regarding the application or nonapplication of the predicates, and (b) context sensitive, which results in constantly shifting lines separating the defined from the undefined cases.