This article reconstructs the hidden dialogue between Johan Huizinga and Carl Schmitt that emerged throughout the 1930s. Huizinga phrased an early critique on Schmitt’s friend-enemy distinction. It appears that throughout the 1930s the Dutch historian had a thorough Auseinandersetzung with Schmitt, running from his In the shadow of tomorrow up to his Homo Ludens. Schmitt, in his turn, responded to Huizinga’s criticism, albeit somewhat implicitly, first, in a small text from 1938 and later in his book on Hamlet. In mapping the emergence of this “dialogue” it appears that their disagreement concerns the relationship between play and war. In particular, they have conflicting ideas on the state of exception, or, to use the German word on which the entire dialogue hinges: Ernstfall. To properly assess the possible relationship between play and war it is first necessary to reconstruct this dialogue and to consider the role of the state of exception within it.