Terrorists come from a wide range of cultures, nationalities, and ideological causes. However, terrorists are similar in their blind allegiance to their cause and their willingness to go to any extreme, including giving their own lives, for that cause. The cause serves as the rationale for joining, but it is not the underlying psychological motivation. The act of joining represents an effort to consolidate identity and to belong. The group provides the core of meaning and identity to the member. Fear of expulsion generates compliance and permits authoritarian structures even in antiauthoritarian groups. However, the intense ambivalence about power and authority helps explain the shifting patterns of leadership often found in terrorist groups. The young average age in some groups indicates that the dynamics of youth contribute to joining the group. The group views the world as consisting of enemies and friends, with the group geared to destruction of enemies (outside society). Acts of terrorism are needed to justify the group's existence and maintain its cohesion. Society's reactive response justifies and reaffirms the terrorist group's views and may promote increased terrorist activity. Thirty-eight reference notes are included.