There are at least two reasons why sustainability of public debt is an issue of increasing importance. First, public choice considerations show the danger of an excessive use of deficit finance in a democracy. Second, the conditions of a European Monetary Union (EMU) imply further incentives for deficit finance. Various approaches to assess sustainability of public debt are presented and partially applied to the EC countries. According to these results, sustainability is as issue of empirical relevance in Europe today and has to be taken seriously on the further way to EMU.