In their collection The Legitimacy of the Middle Ages, Andrew Cole and Vance D. Smith highlighted the ‘medieval turn’ in contemporary critical theory. 1 How to read this turn remains controversial. On some accounts, the modern is founded on a rejection of the medieval. Yet, while the rhetorical rejection of the medieval might be viewed as a constitutive element of critical theory’s self-construction, as also in the case of other projects of modernity—secularization, capitalism, liberal democracy—medieval thought-forms may remain embedded in its systems of argument. The medieval lives on within critical theory, helping to shape it and give it coherence in ways that are not adequately captured by mere negation. In the same collection, Charles Blanton suggests that ‘[m]odernity is nothing more than the necessary accident of unfinished medieval business,’ and notes that much critical theory is concerned ‘with what the medieval renders possible.’ 2 Affect theory is a case in point. As this volume shows, affectus was central to a range of medieval and early modern practices, social formations, and complex moral psychologies, but medieval and early modern thinkers did not exhaust the potentiality of the concept, providing rich sources for later thinkers.