People can have or lack ‘integrity’. But can public institutions? It is common to speak of the ‘integrity’ of such institutions: in popular discourse, legal decisions, law and regulations, and also increasingly, political theory, and proximate disciplines. Such integrity is often said to be at risk of being ‘subverted,’ ‘corroded,’ and ‘corrupted,’ by both forces within and without. Furthermore, the implication is that this is a very worrying thing. The integrity of our institutions, at least, needs to be preserved, supported, (...) and defended; against money, politics, power, and populists. However, despite such common usage, the concept itself has attracted little theoretical reflection. What can it mean, if anything sensible, for an institution itself – instead of a person (or even say, a body, process, territory or a bridge) – to have ‘integrity’? And, why might it be so important? This is the subject of this paper. It puts forward a substantive moral conception of institutional integrity as the robust disposition of an institution to pursue its purpose efficiently, within the constraints of legitimacy, consistent with its commitments. It argues that it is important because it provides the strongest grounding for a ‘duty of support’ owed by citizens to the institution. The strength of such support owed also gives content to a scalar dimension of the institution’s normative legitimacy, that is, the ‘strength’ (or weakness) of such legitimacy. Further, it illustrates how such a conception of institutional integrity will helpfully advance the current debate regarding institutional corruption. (shrink)