Eating behaviour is strongly influenced by social context. We eat differently when we are with other people compared with when we eat alone. Our dietary choices also tend to converge with those of our close social connections. One reason for this is that conforming to the behaviour of others is adaptive and we find it rewarding. Norms of appropriate eating are set by the behaviour of other people, but also shared cultural expectations and environmental cues. We are more likely to follow an eating norm if it is perceived to be relevant based on social comparison. Relevant norms are set by similar others and those with whom we identify. If a norm is relevant then there may be matching of behaviour to the norm, but this will depend on other factors, such as how much attention is paid to the norm, how concerned we are about social acceptance and the presence of other competing norms such as personal norms and consumption stereotypes. Norm matching involves processes such as synchronisation of eating actions, consumption monitoring and altered food preferences. There is emerging evidence that social eating norms may play a role in the development and maintenance of obesity. Social eating norms constitute a novel target for interventions to encourage healthier eating.