Florian Witold Znaniecki (15 January 1882 – 23 March 1958) was a Polish-American philosopher and sociologist who taught and wrote in Poland and in the United States. Over the course of his work he shifted his focus from philosophy to sociology. He remains a major figure in the history of Polish and American sociology; the founder of Polish academic sociology, and of an entire school of thought in sociology. He won international renown as co-author, with William I. Thomas, of the study, The Polish Peasant in Europe and America (1918–1920), which is considered the foundation of modern empirical sociology. He also made major contributions to sociological theory, introducing terms such as humanistic coefficient and culturalism.

In Poland, he established the first Polish department of sociology at Adam Mickiewicz University where he worked from 1920 to 1939. His career in the US begun at the University of Chicago (1917 to 1919) and continued at Columbia University (1932 to 1934 and 1939 to 1940) and at the University of Illinois at Urbana-Champaign (1942 to 1950). He was the 44th President of the American Sociological Association (for the year 1954).