A range of phenomena scholars of battlefield coalitions study, from multinational command-and-control structures to information-sharing agreements, constitute international institutions by definition. Explicitly conceptualising them as such brings attention to how they vary along key dimensions used to study institutions in other contexts: formalisation, membership, scope, control, and centralisation. Drawing on a range of empirical examples from the twentieth and twenty-first centuries, this chapter argues using these dimensions to measure variation across and within coalition cases can generate new avenues for future research. Doing so can bridge the study of battlefield coalitions with scholarship on the dynamics of coalition politics in other types of international institutions.