Abstract: Horizontal equity -- the command that equals be treated equally -- has received increased attention, particularly in attempts to measure the desirability of tax reform proposals. This paper questions whether the normative foundations for horizontal equity justify the indexes and approaches that have generally been adopted. It suggests that past attempts to implement horizontal equity are inconsistent with its supposed foundations and that more thorough examination of the concept raises serious doubts as to whether any alternative interpretation of horizontal equity reasonably consistent with common understanding of the concept can be justified.