Structural data when allied to rich behavioural data offer an important resource for studying adaptive changes in the human brain contingent on the use of more than one language. In our commentary on the review paper by García-Pentón et al. (2015. The neuroanatomy of bilingualism: How to turn a hazy view into the full picture. Language, Cognition and Neuroscience.) we emphasise that data from a variety of methods already converge in identifying key regions subject to adaptive change. With richer characterisations of individual differences in language use more specific predictions can be tested (e.g. on fronto-cerebellar circuits) and such characterisations can in turn inform intervention studies to help specify the causal bases of adaptive change. In the meantime there is great research value in neuroanatomical studies of richly characterised cross-sectional samples of bilingual and multilingual speakers.