The volume contains new essays on Wittgenstein and on Quine. Six essays discuss crucial aspects of Wittgenstein’s philosophy of mathematics: Wittgenstein’s ontological quietism in relation to the realism vs. anti-realism debate, his thesis that mathematical propositions are rules of grammar, his perspectives on the nature of numbers, and on equinumerosity and surveyability, his treatment of mathematical formulas, and his disagreements with Brouwer over the infinite and the law of excluded middle. Six essays are dedicated to the philosophy of Willard Van Orman Quine: they discuss Quine’s stance towards the notion of meaning in linguistics and philosophy, his thesis of the indeterminacy of radical translation, his naturalism in semantics, his brand of nominalism, and his attempt to reconstruct possible worlds within an extensionalist framework. Contributors are: Oswald Chateaubriand, Pasquale Frascolla, Dirk Greimann, Peter Hylton, Guido Imaguire, Mathieu Marion, Felix Mühlhölzer, Mitsuhiro Okada, Esther Ramharter, Ian Rumfitt, Pedro Santos, Severin Schroeder, Rogério Passos Severo.