The Uniqueness Thesis holds, roughly speaking, that there is a unique rational response to any particular body of evidence. We first sketch some varieties of Uniqueness that appear in the literature. We then discuss some popular views that conflict with Uniqueness and others that require Uniqueness to be true. We then examine some arguments that have been presented in its favor and discuss why permissivists (i.e., those who deny Uniqueness) find them unconvincing. Last, we present some purported counterexamples that have been raised against Uniqueness and discuss some possible reasons why proponents of Uniqueness might find these similarly unconvincing.