Territoriality, or territorial behavior, is related to occupation or ownership and control of a geographical area. A territory is a spatial unit that is defended from encroachment. In contrast to personal space, conceived by the anthropologist Edward T. Hall as an area or “bubble” that moves with a person, a territory is a region that is fixed. Topics of interest to social psychologists are how different kinds of territories affect social behavior and the consequences of territorial invasion. This entry examines the background of the idea of territoriality and some relevant research.