This article explores Francesco Guicciardini’s concept of the imagination and argues that it plays a vital, yet hitherto unexplored, role in his political thought. What are called “imaginary conceptions” determine the effects that different governmental strategies have upon a given society. As these both affective and cognitive conceptions are tied to shared, symbolic representations, understanding informal aspects of political life becomes a crucial aspect of Guicciardini’s construal of effective government. To understand these aspects it is necessary to reconstruct the historical genesis of the communal representations as it determines the specificity of the society under consideration. The historical contingency of a society’s imaginary conceptions forces political theory to “imaginatively construct” the institutional forms it suggests, rather than “discover” them among the exempla of the past. The centrality of contingent, imaginary conceptions to political reality leads Guicciardini to break with former Renaissance conceptions of exemplarity.