Williams syndrome, a rare disorder caused by hemizygous microdeletion of about 28 genes on chromosome 7q11.23, has long intrigued neuroscientists with its unique combination of striking behavioural abnormalities, such as hypersociability, and characteristic neurocognitive profile. Williams syndrome, therefore, raises fundamental questions about the neural mechanisms of social behaviour, the modularity of mind and brain development, and provides a privileged setting to understand genetic influences on complex brain functions in a 'bottom-up' way. We review recent advances in uncovering the functional and structural neural substrates of Williams syndrome that provide an emerging understanding of how these are related to dissociable genetic contributions characterized both in special participant populations and animal models.