Some people are more likely to display inflexible, habitual behaviour than others. A diffusion tensor imaging study showed that inter-individual differences in habitual versus goal-directed action control in an instrumental learning task were associated with differential connectivity in corticostriatal networks. Specifically, the strength of white matter tracts between the ventromedial prefrontal cortex and caudate predicted the likelihood of flexible, goal-directed behaviour, and tract strength between the premotor cortex and posterior putamen predicted the likelihood of habitual behaviour. The data suggest that inter-individual differences in tract strength may underlie inter-individual susceptibility to conditions associated with habitual behaviour, such as addiction.