Social interaction is a feature of every aspect of human life. Deficits causing impairment in social function can have a debilitating effect in someone’s life and are prominent in many neuropsychiatric disorders, such as autism and schizophrenia. This has provided a strong impetus to understand the neural substrate of social behaviour with a view to developing effective treatments. This task has been hindered by the complexity of human social interactions. Nonetheless, animal research since the 1970s has identified a class of molecules that play a key role in the development and regulation of social behaviour and its neural substrate.