Following the recent economic and financial crisis, public debt ratios increased considerably in most European Union countries, reaching historically high levels. Against this background, issues regarding the outlook for the debt ratio and the analysis of the sustainability of public finances in Member States became central in the economic policy analysis of European authorities. This Occasional Paper aims to address, in an integrated manner, the various aspects of the discussion on public debt sustainability, with a particular focus on the Portuguese case and on the constraints associated with the institutional and economic environment in the euro area. In this respect, the text approaches the concepts and methodologies used to assess sustainability, lists the existing assessment rules for euro area countries, presents its results for Portugal and refers to the main ongoing discussions on high debt levels.