This chapter presents a methodology for constructing an interpersonally comparable measure of individual well-being, the “extended preferences” approach. It builds upon John Harsanyi’s work. The key idea is that an ethical deliberator makes (or at least is capable of making) judgments concerning the well-being levels of histories and well-being differences between histories—where a history is a hybrid bundle consisting of possible attributes an individual might have, plus possible preference (“tastes”) regarding such attributes. These judgments are represented by a well-being measure. If the deliberator adopts a preference-based conception of well-being, the functional form of that well-being measure can be partly inferred from the utility functions representing the tastes incorporated in histories. That is: the deliberator partly infers what the well-being numbers she assigns to histories must be, given her deference to individual tastes. The chapter also compares the extended-preferences approach to competing methodologies for measuring well-being, in particular the equivalent-income concept.