The term 'social brain' refers to the network of brain regions that are involved in understanding others. Behaviour that is related to social cognition changes dramatically during human adolescence. This is paralleled by functional changes that occur in the social brain during this time, in particular in the medial prefrontal cortex and the superior temporal sulcus, which show altered activity during the performance of social cognitive tasks, such as face recognition and mental-state attribution. Research also indicates that, in humans, these parts of the social brain undergo structural development, including synaptic reorganization, during adolescence. Bringing together two relatively new and rapidly expanding areas of neuroscience--social neuroscience and the study of brain development during adolescence--will increase our understanding of how the social brain develops during adolescence.