This paper aims to resolve the recent debate over whether belief is incompatible with inquiry. I first argue that belief that p is either metaphysically or rationally compatible with merely having some doubt about whether p, whereas it is incompatible with being in doubt about it. Being in doubt about whether p is a stronger way of being uncertain about whether p than having some doubt about whether p. One has some doubt about whether p if and only if one is neither certain that p nor certain that not-p. But being in doubt about whether p also requires being in a state that disposes one to be reluctant to take a stand on whether p. I then motivate the idea that inquiry is an activity of resolving doubt and, as such, is sustained by doubt. Since doubt comes in two varieties, inquiry can be sustained by two kinds of doubt. Inquiry into whether p is incompatible with belief that p when it is the inquirer’s being in doubt about whether p that sustains inquiry, However, it is compatible with belief that p when it is the inquirer’s having some doubt about whether p that sustains it.