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.