Hintikka’s Knowledge and Belief from 1962 is considered the seminal treatise on epistemic logic. It provides the nuts and bolts of what is now a flourishing paradigm of significance to philosophy, economics, mathematics and theoretical computer science—in theory as well as practice. And in theory and for practice epistemic logic has been extensively articulated, refined and developed especially with respect to capturing the dynamics of reasoning about knowledge. But although the robust narrative about Hintikka’s epistemic logic is rather static, the leap to dynamic epistemic logic is right there back in 1962 as this paper will show.