Contemporary epistemologists have devoted considerable attention to conceptual analyses of the nature of epistemic justification but there is great disagreement about whether the factors relevant to the justification of a person’s belief must be internally accessible to that person (Alston 1989; Fumerton 1996; Kornblith 2001; Pryor 2001; BonJour and Sosa 2003; McGrew and McGrew 2006; Goldberg 2007; and Poston 2008). This debate between internalists, who endorse the access requirement, and externalists, who reject it, has been little discussed by philosophers of science.[i] Yet epistemic justification is a central concern in philosophy of science. In particular, the wide-ranging debates over evidence and confirmation seem to be concerned to a significant degree with the question of justifying conclusions from data. Theories of evidence can indeed be understood in part as attempts to explicate a concept of scientific justification. But how do such theories depict scientific justification? Do they employ an internalist or externalist notion of justification? To facilitate an inquiry into these questions we reconsider the dichotomy between internalism and externalism from the perspective of justificatory practices in the sciences. In doing so, we find that the dichotomy as traditionally formulated does not adequately capture the nature of justification in scientific inquiry. We motivate our reformulation by attending to the socially-situated nature of practices of scientific justification. As part of this reformulation, we redirect the debate away from a concern with the justification of beliefs and toward the justification of assertions of experimental inferences. Such a redirection has a further basis in the nature of our inquiry, which considers the question of justification from the perspective of objective accounts of scientific evidence. More precisely, we are concerned with theories that treat evidential relationships as obtaining in a manner that is epistemically independent of the beliefs of particular individuals or groups...