Many are now discussing the possible demise of the so called ‘liberal international order’, but how can we know whether any international order is changing? This article argues for understanding order as maintained by institutions of international society and further theorises the role those institutions play in the stability or transformation of international order. To usefully put institutional analysis to work, this article, first, models the stylised evolution of a primary institution. Second, it illustrates this evolution with a discussion of the historical institution of trusteeship in order to historicise adaptation and transformation in international order. Finally, this leads to a generalised idea of how institutional analysis can be employed to study stability and transformation in international order. Beyond making a contribution to the wider debates about the possible demise of the current international order, this piece also fills a gap in English School theory, which is quite silent on the question of when international society furthers transformation, and when it furthers stability. Accepting the view of history that the future is contingent on today’s events, this study suggests possible points where push comes to shove for change and continuity in international order more generally.