Cross-cultural psychology is the scientific study of human behavior and mental processes, including both their variability and invariance, under diverse cultural conditions. Through expanding research methodologies to recognize cultural variance in behavior, language, and meaning it seeks to extend and develop psychology. Since psychology as an academic discipline was developed largely in North America and Europe, some psychologists became concerned that constructs accepted as universal were not as invariant as previously assumed, especially since many attempts to replicate notable experiments in other cultures had varying success. Since there are questions as to whether theories dealing with central themes, such as affect, cognition, conceptions of the self, and issues such as psychopathology, anxiety, and depression, may lack external validity when "exported" to other cultural contexts, cross-cultural psychology re-examines them using methodologies designed to factor in cultural differences so as to account for cultural variance. Although some critics have pointed to methodological flaws in cross-cultural psychological research and claim that serious shortcomings in the theoretical and methodological bases used impede rather than help the scientific search for universal principles in psychology, cross-cultural psychologists are turning more to the study of how differences (variance) occur, rather than searching for universals in the style of physics or chemistry.
While cross-cultural psychology represented only a minor area of psychology prior to WWII, it began to grow in importance during the 1960s. In 1971, the interdisciplinary Society for Cross-Cultural Research (SCCR) was founded, and in 1972 the International Association of Cross-Cultural Psychology (IACCP) was established. Since then, this branch of psychology has continued to expand as there has been an increasing popularity of incorporating culture and diversity into studies of numerous psychological phenomena.
Cross-cultural psychology is differentiated from cultural psychology, which refers to the branch of psychology that holds that human behavior is strongly influenced by cultural differences, meaning that psychological phenomena can only be compared with each other across cultures to a limited extent. In contrast, cross-cultural psychology includes a search for possible universals in behavior and mental processes. Cross-cultural psychology "can be thought of as a type [of] research methodology, rather than an entirely separate field within psychology". In addition, cross-cultural psychology can be distinguished from international psychology which centers around the global expansion of psychology especially during recent decades. Nevertheless, cross-cultural psychology, cultural psychology, and international psychology are united by a common concern for expanding psychology into a universal discipline capable of understanding psychological phenomena across cultures and in a global context.