This article explores the impact of biological psychiatry as the present dominant frame for understanding mental disorder on legal rules and practices. It begins with a brief overview of biological psychiatry, showing that biological understandings of mental disorder have ancient origins in Western thought, but have ebbed and flowed in popularity over time, coexisting sometimes acrimoniously with other models of mental disorder. This section presents and explains the dominance today of neuroscientific approaches within a historical context. I then present ways in which I suggest that the neurobiological model of mental disorder will affect the law in five areas: evidence of mental states, the definition of disability in human rights law, criminal responsibility, the regulation of brain interventions, and the regulation of reproductive technologies. Some of these are admittedly speculative, but are advanced as suggestions for further attention as neuroscientific research proceeds and is incorporated within social institutions and practices, such as the law.