This volume contains ten new essays on a priori knowledge by authors from Canada, the United States, Australia, & Europe Topics addressed include the nature, explanation, & indispensability of a priori knowledge, its connection with analytic truth, its place in mathematics, in logic, & in empirical theory, & the contribution of Kant & Quine to these topics. The focus is on twentieth-century contributions to these issues, but most essays also address earlier discussions at some length, & the essays that focus on Kant also relate his views to more recent discussions. Contents: Introduction. A Rationalist Manifesto. Analyticity, Undeniability, & Truth. Analyticity & the A Priori. The Doubtful A Priori. Some Remarks on Indiscernibility. The Constitutive A Priori. Kant's A Priori Methods for Recognising Necessary Truths. EPR as A Priori Science. Gaps, Gluts, & Paradox. An Essay on Material Necessity.