Polish-American sociologist whose theoretical and methodological work helped make sociology a distinct academic discipline. He was a pioneer in the field of empirical investigation and was noted as an authority on Polish peasant culture.

Znaniecki's earliest work was as a poet. After being expelled from the University of Warsaw for his active support of Polish nationalism, he studied at various universities in France and Switzerland and received his doctorate in philosophy from the University of Kraków in 1909. Under the influence of the American sociologist W.I. Thomas, he turned to sociology, joining Thomas at the University of Chicago (1914), where they began their joint work, The Polish Peasant in Europe and America, 5 vol. (1918–20). This work made significant advances in methodology (notably in the use of intensive life histories) as well as in substance (a framework for the sociological view of personality and a study of immigrant social disorganization).

Znaniecki returned to Poland in 1920 and became professor of sociology at Poznań, where in 1922 he founded a sociological institute. He wrote several books in Polish, including an introduction to sociology and a work on the sociology of education; The Laws of Social Psychology (1925); The Method of Sociology (1934); and Social Actions (1936). A series of lectures delivered at Columbia University was published as The Social Role of the Man of Knowledge (1940). The outbreak of World War II prevented Znaniecki's return to Poland, and he joined the faculty at the University of Illinois, Champaign-Urbana, where he wrote Cultural Sciences, Their Origin and Development (1952) and Modern Nationalities (1952).