This paper concerns Wittgenstein’s conception of philosophical and mathematical problems. Both in his earlier and in his later writings Wittgenstein grapples with the tendency of philosophers to misconstrue the nature of the difficulties that they are facing. Whereas philosophers tend to assume that their problems are comparable to those that come up in the sciences, and take these problems to consist in questions the answers to which will provide them with substantive knowledge, Wittgenstein compares philosophical problems with riddles. What is (...) characteristic of riddles is that solving them involves an alteration of the use of language, but it does not tend to involve the acquisition of new knowledge. In his middle and later period, the comparison with riddles serves to highlight and resolve a related confusion in the way philosophers of mathematics understand the nature of mathematical problems. Wittgenstein rejects the realist approach according to which every mathematical theorem, whether proven or not, meaningfully specifies a possible fact which would make it true or false. By contrast, Wittgenstein construes unproven conjectures on the model of riddle phrases, whose meaning, prior to our finding the solution to them, has not been determined. Moreover, Wittgenstein draws our attention to the fact that we can be caught up in an attempt to solve a riddle even if the riddle does not have a solution; the same applies, in his mind, to our engagement with philosophical and mathematical problems. When it comes to philosophical riddles, Wittgenstein is convinced that they do not have a solution at all. The specific difficulty presented by unproven mathematical conjectures is different; in this case, we cannot tell in advance whether or not they present us with a solvable riddle. The paper situates these issues in the context of ongoing debates in the scholarship concerning Wittgenstein’s conception of nonsense, his methodology, his engagement with mathematical realism and verificationism, and his response to skepticism. (shrink)