Hans Kelsen (; October 11, 1881 – April 19, 1973) was an Austrian jurist, legal philosopher and political philosopher. Due to the rise of Nazism in Germany and Austria, Kelsen left his university post because of his Jewish ancestry, and departed to Geneva in 1933, and then to the United States in 1940. In 1934, Roscoe Pound lauded Kelsen as “undoubtedly the leading jurist of the time.” While in Vienna, Kelsen was a young colleague of Sigmund Freud and wrote on the subject of social psychology and sociology.