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The current academic and political debate about the quality of tax systems does not systematically take into account aspects of sustainability. For some time now, OECD, International Monetary Fund and European Commission have been pushing the case for enhancing the growth-friendliness of tax systems. Ecological and social/equity considerations appear to have lower priority in the hierarchical order of objectives guiding the recommendations for the design of tax systems. The European Commission and the OECD regularly publish an increasing number of indicators and the underlying data that can be used to assess different sustainability dimensions of tax systems and/or individual tax categories also in a cross-country comparison and over time. In particular, the European Commission has developed a set of indicators trying to capture the contribution of member states’ tax systems to the goals of the Europe 2020 strategy. This set of indicators, however, focuses on the growth-friendliness of member states’ tax systems, while indicators for their distributional and environmental impact play a less prominent role. The paper attempts at establishing a conceptual basis for the development of a consistent set of indicators to capture the sustainability impact of tax systems. Firstly, we formulate fundamental objectives underlying a sustainable tax system. Then we present some fundamental deliberations about the function of indicators and a classification of indicators which may be useful to assess the sustainability impact of tax systems. Against this background, we critically review the European Commission’s indicator-based approach to evaluate EU member states’ tax systems within the European Semester. Finally, we address open questions and next research steps.