It is commonplace to distinguish between propositional justification (having good reasons for believing p) and doxastic justification (believing p on the basis of those good reasons).One necessary requirement for bridging the gap between S’s merely having propositional justification that p and S’s having doxastic justification that p is that S base her belief that p on her reasons (propositional justification).A plausible suggestion for what it takes for S’s belief to be based on her reasons is that her reasons must contribute causally to S’s having that belief. Though this suggestion is plausible, causal accounts of the basing relation that have been proposed have not fared well. In particular, cases involving causal deviancy and cases involving over-determination have posed serious problems for causal accounts of the basing relation. Although previous causal accounts of the basing relation seem to fall before these problems, it is possible to construct an acceptable causal account of the basing relation. That is, it is possible to construct a causal account of the basing relation that not only fits our intuitions about doxastic justification in general, but also is not susceptible to the problems posed by causal deviancy and causal over-determination. The interventionist account of causation provides the tools for constructing such an account. My aim is to make use of the insights of the interventionist account of causation to develop and defend an adequate causal account of the basing relation.