In response to the Eurozone sovereign debt crisis, policymakers have initiated a range of reforms falling at both poles of the “hard”/“soft” law continuum. One of the most ambitious is the United Nations Conference on Trade and Development’s initiative to identify what it calls “Principles of Responsible Sovereign Lending and Borrowing.” The Principles aim to transform attitudes about sovereign lending in general, and sovereign loan contracts in particular, through consensus-building, promulgating model contract terms, and other soft law approaches. Principle 15, for example, envisions the use of collective action clauses (CACs) to ensure that debt restructurings occur “promptly, efficiently, and fairly.” Public officials agree with this goal, if not the method. Eschewing persuasion and other soft-law techniques, Eurozone leaders have stated their intent to mandate the use of standardized CACs in all euro area sovereign bonds. This article explores, and ultimately questions, whether initiatives such as the Principles are likely to have a significant impact on bond contracts. Over the past century, other initiatives have pursued the same goal with varying degrees of success. Using a dataset of bonds issued in New York and London, the article demonstrates how contracts responded (or failed to respond) to these initiatives, often in ways reformers did not anticipate. Several lessons emerge. First, initiatives designed to encourage changes to entrenched contracting practices may require significant and coordinated leadership by states and other international actors. Without such leadership, these initiatives may fail. One reasons for this is that reformers often misread market sentiment or fail to appreciate the diverse preferences of market actors. Second, even successful initiatives can have unexpected results. In particular, efforts to encourage the use of uniform contract terms may have the paradoxical effect of provoking greater contract variation. The third lesson, then, is that standardization – assuming that is a desirable (and feasible) goal – may have to be mandated. The paper concludes by exploring other ways in which initiatives like the Principles can influence sovereign lending markets.