Processes and outcomes in sovereign debt governance result from the interaction of heterogeneous and interdependent actors, be they sovereign debtors, creditors, or their respective constituencies. There are several sources of actors’ heterogeneity: the economic and institutional profiles of borrowing countries, their constituencies’ preferences over fiscal policy options, and the lending frameworks and credit exposures of creditors. At the same time, borrowing countries exist and operate within a broader set of institutions, and creditors operate in the shared environment of global finance—this gives rise to interdependence, both within and between actors. Importantly, heterogeneity and interdependence are defining features of what is called a complex adaptive system—i.e., an environment where diverse actors interact with, and adapt to, one another via a web of connections. This thesis thus takes a complex systems perspective, and considers: (i) how sovereign debtors’ integration in an international political economy creates channels of transmission for the spread of debt crisis resolution policies; (ii) how repeated interactions between debtors, creditors, and their constituencies at debt talks create feedback effects that might nonlinearly aggregate; and (iii) how the involvement of creditors with different lending paradigms in the development landscape opens the room for interaction dynamics other than competition. In all three cases, results point to the relevance of heterogeneity and interdependence in shaping patterns of borrowing and lending behaviour, as they provide new evidence on debtor-creditor, inter-debtor and inter-creditor relations.