Impelled by the danger of nuclear war, psychologists, especially in the United States, have been trying since World War II to make an expert contribution to the healing of international ills. Such a contribution might provide psychological insights into social and political phenomena and enrich our understanding of certain aspects of international life. It will be particularly useful if we realize the limitations of psychological explanation, refrain from going too far in looking at international phenomena from a psychologist’s point of view and avoid apolitical explanations which ignore the political aspects of competition between States.