Gaining an understanding of crowd behavior is important in supporting timely and appropriate crowd management principles in the planning and provision of emergency services at mass gatherings. This paper provides a review of the current understanding of the psychological factors of a crowd within the psychosocial domain as they apply to mass-gathering settings. It can be concluded from this review that there is a large theory-practice gap in relation to crowd psychology and the mass-gathering setting. The literature has highlighted two important elements of crowd behavior-there must be a "seed" and people must engage. Understanding these behaviors may provide opportunities to change crowd behavior outcomes.