This article examines the ambivalent, or even contradictory, status of the notion of lack in Jacques Derrida’s work in order to reconstruct what I call the “vicarious logic” of lack/supplementarity. Within this logic, lack is understood not as the negative absence of plenitude, but as the lack of a supplement and thus as the site of a representative logic of referentiality. Because the problem of lack is approached here through the question of self-relationality, the article, while drawing on Derrida’s other major writings, centres on a close reading of Voice and Phenomenon.