This chapter addresses tax knowledge, where it comes from and how it is used and understood. Scholarly tax knowledge, as distinct from the tax knowledge of laypersons, varies in many ways, the premises on which it is based, the prior knowledge that is built upon, how it is used by other scholars and in practice by policymakers and others. We describe scholarly tax knowledge in topographical terms, to highlight the distinctions between academic disciplines. We also point to some areas where traps await the unwary, who may not be fully aware of the underlying assumptions and special language used within particular disciplines. Finally, we describe our own approach to generating tax knowledge, using ethnographic methods, an interpretive approach and a critical eye.