While the increasingly thick web of global, regional and sub-regional security arrangements and institutions has received ample scholarly attention, the phenomenon of ad hoc military coalitions and how they impact these institutions has been relatively little explored. We examine ad hoc coalitions in international security responses and develop a tentative typology of military responses that takes ad hoc coalitions into consideration, where we differentiate in terms of institutionalisation and duration. Following a rational-choice institutionalist logic, we argue that institutional proliferation increases the chances of institutional exploitation. We illustrate this with how states apply a pick-and-choose approach in which institutional products but not frameworks are used. They use the interoperable forces, a common culture and mainstreamed doctrine, but not the formal deployment of rapid response mechanisms of eg the North Atlantic Treaty Organization and the African Union. In closing, we observe that institutional proliferation in international security facilitates a functionalist approach mainly inspired by national self-interest. Future research should examine whether this could result in dwindling relevance of international institutions, first in the domain of security, but later also in other domains.