In this chapter, we perform a conceptual analysis of a household sustainable consumption index, whose construction is based on guidelines in a handbook issued by OECD. We conclude in our analysis that the designers of the index treat the concept ‘sustainable consumption’ as a descriptive concept, and argue that this interpretation is a conceptual mistake. A consequence of this mistake is that the construction of the index is treated as a kind of statistical and empirical problem only. Instead, we argue that sustainable consumption is a specific kind of value concept named intermediate concept, whose function is to link descriptive grounds with normative consequences, and thus that the construction of the index is a normative problem. That is, the construction of a sustainable consumption index should be regarded as a normative multi-attribute decision process. A policy implication of our study is that when measuring sustainability, a decision analytic approach based on an adequate interpretation of the concept sustainability as an intermediate concept should be employed. In order to avoid low validity of sustainability indices as a result of making a conceptual mistake, it is possible to explicitly treat the construction of a sustainability index as a normative multi-attribute decision process that can be aided by decision support tools. The relevance of our analysis to policymakers and other stakeholders is that it contributes to a deeper understanding of what kind of concept sustainability is and what it means to measure such concepts. Without a proper understanding of the nature of this concept, there is an obvious risk of low validity of its measurement.