This paper assesses the various definitions and mechanisms used to achieve debt sustainability. Section 2 examines the basis for the definition of sustainability currently used by the international community to determine debt relief levels and monitor long-term sustainability. Section 3 examines the different methods used to assess sustainability, using equations, models and thresholds. Section 4 looks at the application of definitions and thresholds to attain debt sustainability for developing countries, by using them as guidelines for providing debt relief and concessional new financing, and for deciding debtor country policies. Section 5 concludes with ideas for how to analyze and achieve genuine long-term debt sustainability in developing countries. These ideas—and the analysis on which they are based – spring largely from the views of finance ministers and debt managers from 38 low-income governments, especially those of HIPCs, which have been expressed repeatedly in meetings organized by the HIPC Debt Strategy and Analysis Capacity-Building Program (HIPC CBP) since 1997.