Multidimensional indices are becoming increasingly important instruments to assess the well-being of societies. They move beyond the focus on a single indicator and yet, are easy to present and communicate. A crucial step in the construction of a multidimensional index of well-being is the selection of the relative weights for the di¤erent dimensions. The aim of this paper is to study the role of these weights and to critically survey eight di¤erent approaches to set them. We categorize the approaches in three classes: data-driven, normative and hybrid weighting, and compare their respective advantages and drawbacks.