Came to the United States, 1939, naturalized, 1944. In charge of applied mathematics laboratory, University of Kiel, 1929-1933. Research associate, University of Stockholm, 1933-1939.
Associate professor and executive editor, Mathematics Reviews, Brown University, 1939-1945. Professor Cornell University, 1945-1950. Eugene Higgins professor of mathematics, Princeton University, from 1950.
Consulting and war work. Visiting professor at Rockefeller University.