The theory of regime complexity offers a useful lens through which to analyse the increasing density of international institutions and the patterns of conflict and cooperation among them. Scholarship on crisis and development finance would benefit from more fully employing this approach to explain the emergence of overlapping institutions and offer recommendations for designing regime complexes. The theory advanced here emphasizes the strategies of key states to use institutional overlap to limit agency ‘drift’ away from their preferences. Prioritizing control often comes at the cost of conflict among the institutions, however, and can thus impede the achievement of financial stability and development goals. The regime complexity approach is distinct from the rational design of institutions, institutional experimentalism and theoretical realism. Drawing on lessons from the euro crisis, this article offers informed conjectures on financial arrangements in the regions of Latin America and East Asia and their interaction with global multilateral institutions, such as the International Monetary Fund.