In 1939, after the "Zentralblatt" was taken over by the Nazis, he moved to the United States, joined the mathematics department at Brown University, and founded "Mathematical Reviews". He became an American citizen and remained at Brown for most of his career, founding the History of Mathematics Department there in 1947 and becoming University Professor. Jointly with the American Assyriologist Abraham Sachs, he published "Mathematical Cuneiform Texts" in 1945, which has remained a standard English-language work on Babylonian mathematics. In 1967, he was awarded the Henry Norris Russell Lectureship by the American Astronomical Society. In 1977, he was elected to the National Academy of Sciences, and in 1979, he received the Award for Distinguished Service to Mathematics from the Mathematical Association of America. In 1984, he moved to the Institute for Advanced Study in Princeton, where he had been a member since 1950.