Originally issued in 1954 and updated in 1961 and 1987, this pioneering study of small group conflict and cooperation has long been out-of-print. It is now available, in cloth and paper, with a new introduction by Donald Campbell, and a new postscript by O.J. Harvey. In this famous experiment, one of the earliest in inter-group relationships, two dozen twelve-year-old boys in summer camp were formed into two groups, the Rattlers and the Eagles, and induced first to become militantly ethnocentric, then intensely cooperative. Friction and stereotyping were stimulated by a tug-of-war, by frustrations perceived to be caused by theout group, and by separation from the others. Harmony was stimulated by close contact between previously hostile groups and by the introduction of goals that neither group could meet alone. The experiment demonstrated that conflict and enmity between groups can be transformed into cooperation and vice versa and that circumstances, goals, and external manipulation can alter behavior. Some have seen the findings of the experiment as having implications for reduction of hostility among racial and ethnic groups and among nations, while recognizing the difficulty of control of larger groups.