Humans, like other primates, are intensely social creatures. One of the major functions of our brains must be to enable us to be as skilful in social interactions as we are in our interactions with the physical world (e.g. recognising objects and grasping them). Furthermore, any differences between human brains and those of our nearest relatives, the great apes, are likely to be linked to our unique achievements in social interaction and communication rather than our motor or perceptual skills. Unique to humans is the ability to mentalise (or mind read), that is to perceive and communicate mental states, such as beliefs and desires. A key problem facing science is to uncover the biological mechanisms underlying our ability to read other minds and to show how these mechanisms evolved. To solve this problem we need to do experiments in which people (or animals) interact with one another rather than behaving in isolation. Such experiments are now being conducted in increasing numbers and many of the leading exponents of such experiments have contributed to this volume. 'The Neuroscience of Social Interactions' will be an important step in uncovering the biological mechanisms underlying social interactions - undoubtedly one of the major programmes for neuroscience in the 21st century.