Abstract This chapter explores the limits on what can be known that are revealed by an argument first published by Fitch, sometimes known as the Paradox of Knowability. The argument shows that if some truths are unknown then some truths are unknowable. This represents an important challenge to verificationism and anti‐realism. Objections to the argument by Edgington, Kvanvig, Melia, and others are considered and projected. Thus, knowledge turns out to have structural limits.