The life cycles of gatherings, demonstrations, and riots begin with an assembling phase and end with a dispersal phase. The three types of events are primarily distinguished by the form and content of individual and collective behaviors that occur in the interim phase when a number of people are in the same locale at the same time. We review the past 15 years’ research on behaviors in this phase. We first consider some elementary forms of collective behavior that frequently occur in all gatherings, demonstrations, and riots. We next examine more complex dimensions and forms of behavior within political, religious, and sport demonstrations. We then review research on the individual and aggregate violence against person, property, and property rights that distinguishes riots. Finally, we note some recurring patterns in the research on all three types of events, and we identify problems warranting further investigation.