This book describes the present status and the history of the International Union of Psychological Science (IUPsyS) -- the most representative international psychological body. The IUPsyS includes national psychological associations from 66 countries, with more joining every year, and it has formal relations with the United Nations, UNESCO, the World Health Organization, the International Council for Science, and the International Social Science Council. Many well known psychologists have played important roles in this international organization, and the text and many photographs bring the story to life. IUPsyS was organized formally at the 14th international Congress of Psychology at Stockholm in 1951, so the 27th International Congress of Psychology at Stockholm in 2000 marks a half-century of its existence. But the history of the IUPsyS goes back to the first International Congresses of Psychology, 1889, and to the International Congress Committee which foreshadowed the organization of the International Union. After describing the present status of the IUPsyS in Chapter 1, the book traces briefly the early development of scientific societies and organizations. Chapter 3 tells how the first International Congress of Psychology was organized in Paris in 1889 and what it accomplished. Successive international congresses and the growth of psychology during the next sixty years are treated in chapters 4-6. The founding and development of the International Union in the last half of the 20th Century are described in the remaining chapters. International Congresses organized by the IUPsyS have taken place regularly since 1951, and the IUPsyS has steadily gained in the scope and influence of its activities. The congresses, long restricted to western Europe and North America, became more representative geographically, moving to Moscow, Tokyo, Leipzig, Acapulco, and Sydney, with the 28th congress planned for Beijing in 2004. The history shows how the IUPsyS has become increasingly able to face the problems and opportunities of the 21st century.