<p>Interest in the scientific study of well-being has grown substantially, spanning various disciplines and sectors of society, while also gaining greater relevance in policymaking. In this Perspective, we compare and contrast unidimensional versus multidimensional understandings of well-being, and corresponding measures of life satisfaction or life evaluation versus flourishing. We consider conceptual, empirical, pragmatic and policy arguments that have been put forward for each of these understandings and measurement approaches. While we argue that well-being needs to be conceptually and scientifically understood, and empirically studied, as a multidimensional construct, we acknowledge the pragmatic and policy challenges of doing so and how in some circumstances relying on a unidimensional assessment may sometimes be practically necessary. We put forward some proposals as to how researchers and policymakers might navigate these various challenges.</p>