This document discusses how society is organized into groups. It defines social groups as collections of interdependent individuals who pursue shared goals. Primary groups are small, intimate groups involving face-to-face interaction over long periods of time, while secondary groups are larger and less intimate with more impersonal, objective-focused relationships over shorter times. Self-categorization theory holds that people define their own group membership based on how they perceive non-members of out-groups compared to their in-group. Social groups are important as they transmit culture, exert social control, socialize individuals, generate ideas, and facilitate communication.