Outdoor music festivals are increasingly common events on the summer entertainment landscape for youth in many countries around the world. Evidence indicates that attendance is associated with risk of injury and death. A considerable proportion of crowd-related risks are attributed to irrational and high-risk behaviour by patrons in the general admission, or standing room only, areas in front of stages, or ‘mosh pits’. Commentators note that many event organisers rely too heavily on previous experience when planning their events and suggest that this approach is often ill structured, piecemeal and ad hoc. While there is considerable endorsement in the literature for a risk management approach, its application to crowd safety is rare. Risk assessments for music festivals and mass gatherings generally tend to deal with the traditional hazards and risks found at most workplaces, without taking into account the dynamics of the crowd or those factors that influence its behaviour. Influences on crowd behaviour are little understood and generally ignored, leaving a significant source of risk at this type of event unaccounted for.A number of commentators recommend that a comprehensive approach to crowd safety assessment, design and management needs to integrate both psychological and engineering frames of reference. To date, the literature on ‘mass gatherings’ has focused on the environmental and biomedical domains, with limited knowledge to support our understanding of the psychosocial domain, including identifiable key features and how these elements interact with each other. This paper outlines the development of a model of collective behaviour that can be used as the basis for developing an appropriate and contextualised methodology and instrument for assessing crowd related risks at outdoor music festivals.