 In this entry, we clarify the concept of a priori knowledge (and related concepts), as well as the relationship between a priori knowledge and analyticity. We then review Kant’s view of moral knowledge, early 20th century versions of non-naturalism, late 20th century versions of naturalism, particularism, and finally some 21st century versions of intuitionism—all with an eye to the role they afford to a priori knowledge.