The article explores the notion of liquid authority by examining the ways in which the central organizations in three transnational regulatory-governance regimes do or do not attempt to establish interpretive control over the norms that they issue: the International Accounting Standards Board, the International Organisation of Standardisation, and the Forest Stewardship Council. The need to ‘solidify’ their authority ranges across all of their regulatory functions; this article focusses on just one of those functions: interpretation. In focussing on how these regulators seek to exercise interpretive control, the article seeks to show how liquid authority can crystallize. Further, the article develops the notion of liquid authority by arguing that the establishment, exercise, and continual maintenance of authority in transnational regulatory regimes, which are characterized by liquid authority as they lack a formal, legal base, are fundamentally linked to the issue of legitimacy. It argues in turn that legitimacy, and thus authority, is endogenously produced, a fact which exogenous, normative assessments of legitimacy can overlook. The article argues that regulators play an active role in their own legitimation – in creating, exercising, and maintaining their legitimacy, and in turn their authority, and that their success or otherwise in doing so is linked in part to their functional effectiveness, but that transnational regulators face a legitimacy paradox: they depend in part on such effectiveness for their legitimacy. The article supplements the ‘anatomical’ analysis of liquid authority with an understanding of the physiology of legitimation.