Objectives. Mass gatherings pose distinctive challenges for medicine. One neglected aspect of this is that the behaviour of people participating in such events is different from the behaviour they exhibit in their everyday lives. This paper seeks to describe a Social Psychological perspective on the processes shaping people's behaviour at mass gatherings and to explore how these are relevant for an understanding of the processes impacting on infection transmission.Conclusions. It is inadequate to conceptualise mass gatherings as simply an aggregate of a large number of individuals. Rather, those present may conceptualise themselves in terms of a collective with a shared group identity. Thinking of oneself and others as members of a collecti...