Until recently the field of psychology has been a monocultural science in a Euro-American envelope. Profound global changes in social, economic, political, and academic development have resulted in a more multicultural perspective for psychology. The field of psychology is now growing more rapidly outside than inside the U.S. As a result of these changes, multiculturalism adds a dimension to psychodynamic, humanistic, and behavioral psychology as much as the fourth dimension of time adds meaning to three dimensional spaces. The contributors to Multiculturalism as a Fourth Force seek to separate what we know from what we do not yet know about the importance of multiculturalism to these changes in the field of psychology. Topics include cultural diversity within and between societies, multiculturalism and psychotherapy, and culture centered interventions. Each contributor describes the need for multiculturalism in psychology, the difficulties in establishing a multicultural perspective and what has to happen before multiculturalism can claim to be a Fourth Force to supplement the other forces for psychology. In addition, the contributors examine the role of culture to the changing field of psychology and provide case examples of this phenomenon. It is the author's hope that by making culture central rather than marginal in the area of psychology, the psychodynamic, behavioral and humanistic theories can become more effective and less culturally biased.