This document discusses collective behavior and social movements. It defines collective behavior as gatherings of two or more people in public places that can include demonstrations, riots, or other behaviors. Behaviors within gatherings can include milling, common focus, locomotion, queuing, and vocalization. Demonstrations are gatherings primarily for protest or celebration, while riots consist mainly of violence against people or property. For social movements to form, they require an existing communications network that can be co-opted by movement ideas as well as organizing efforts to unite spontaneous groups. Examples discussed include the civil rights movement, women's liberation movement, Arab Spring, and Occupy Wall Street.