This article explores the contemporary scientific practice of human genome science in light of Michel Foucault’s articulation of the problem of population. Rather than transcending the politics of social categories and identities, human genome research mobilizes many different kinds of populations. How then might we aim to avoid overgeneralized readings of the refiguring of human difference in the life sciences and grapple with the multiple and contradictory logics of population classification? In exploring the study of human variation through the case (...) of the ‘Quebec founder population’ at a private genome research laboratory in Canada, the article argues that the power to define and shape meanings of human variation and to organize vitality is not held by any one institution or form of scientific practice. While molecular genomics may be transforming conceptions of human difference, the laboratory is only one of many places where human genomic variation accrues value, meaning and relevance. Molecular configurations of human difference gain meaning through a traffic in populations that extends beyond the laboratory. In the case explored here this traffic in populations is constituted within a nexus of empire, national census practices and contemporary articulations of multicultural policies. (shrink)