Urban sustainability has been revealed as one of the key elements in achieving global sustainability. There is a wide range of indicators in this field; however, sustainability indicators have not been exempt from criticism, in both their formal aspects and practical usefulness. If measuring sustainability is "measuring the immeasurable", then the objective of this article is to propose a composite indicator that evaluates only the deficits of sustainability or, which is the same thing, the

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... stainability of cities. This focus has the advantage of showing up the particular deficiencies and thus the priorities that each city must attend to. For this purpose, only unsustainability, defined as the distance to a sustainability target, was considered. Aggregation was carried out through generalized means, which lead to a proper balance between compensatory and non-compensatory aggregation. The results emerging from the application of our methodology to a sample of fifty different cities suggest that all cities should attend to some aspect concerning sustainability, and that no city is sustainable, but only less unsustainable, showing both significant differences between cities in terms of the degree of unsustainability and a common underlying structure of unsustainability in which the environmental dimension contributes the most.