Despite new interest in the implications of growing institutional density for international cooperation, and in so-called public private governance, the interplay between public and private regimes has so far been largely overlooked. This article draws on the emerging literature on parallel regimes in international governance to analyze the evolution of the norms and rules governing sovereign debt restructuring from the early 1980s to the mid-2000s, with a particular focus on the interplay between those covering official bilateral (or Paris Club) debt, and those dealing with private credits. It shows how, from the mid-1990s onward, changes in market and political environments turned burden sharing between bilateral and private creditors into a contentious issue, partly undermining the existing framework for public-private cooperation, and confirms that a focus on institutional interplay can help identify some of the key dynamics behind public-private cooperation. Keywords: parallel regimes, institutional interplay, public-private governance, sovereign debt restructuring, Paris Club. ********** Acknowledging the multiplication of international agreements and norms, scholars have begun to question the implications of growing institutional density for international cooperation. (1) Concepts such regime overlap, nesting, or regime complex have been developed to attempt to account for the phenomenon, and explore its consequences. Yet while the interplay between state-led regimes has attracted rising scholarly attention, that between private regimes, or between state and private regimes, has remained virgin territory, despite early calls for a thorough analysis. (2) In light of the growing interest in issues relating to public-private governance, the fact that the interaction between state and nonstate sets of principles, norms, and rules has largely been overlooked seems especially puzzling. One reason might be the lack of a clear line between state and nonstate. Virginia Haufler identifies a private regime as one in which co-operation among private actors is institutionalized, and in which states do not participate in formulating the principles, norms, rules or procedures which govern the regime members' behaviour. (3) However, private regimes, like their exclusively state-led counterparts, are best seen one end of a continuum along which the proportion of state and private influence varies. In some areas, regimes are created by states on private foundations (e.g., human rights); in others, regimes are established by private actors under the watchful eye of the state (e.g., maritime insurance or Internet access). In yet others, state and private actors share in the definition, implementation, and monitoring of norms and rules (e.g., intellectual property rights or the Basel II framework). Yet when focusing on the two ends of the continuum (i.e., contrasting primarily state-led and primarily private-led institutional arrangements), important differences emerge that may influence institutional design and evolution. In particular, whereas market actors are primarily accountable to their shareholders and investors and therefore must obey commercial imperatives, state actors are subject to electoral accountability and their decisions tend to reflect geopolitical considerations and domestic political pressures. How these differences impact the interplay between public and private regimes, creating synergy or conflict, is thus of major interest. Drawing on the emerging literature on parallel regimes in international governance, I analyze the evolution of the bilateral and private regimes for sovereign debt restructuring from the early 1980s to the mid-2000s, with a particular focus on the interplay between the two. As will be shown below, the existence of different sets of norms and practices governing official bilateral and commercial debt first attracted scholarly interest in the 1980s, with the Latin American debt crisis. …