There are at least as many views on how the welfare of individuals should be compared as there are authors who write on the subject. An indication of the bewildering range of issues considered relevant in the literature is provided by the book Interpersonal Comparisons of Well-Being (Elster & Roemer 1991). However, this article plans to interpret the interpersonal comparison of utility narrowly. Although it reviews some traditional approaches along the way, its focus is on what the modern economists mean when they talk about units of utility and how can such utils be compared. It is widely thought that utils assigned to different individuals cannot sensibly be compared at all.