Hörmander was given a position as part-time professor at Stanford in 1963, but was soon thereafter offered a professorship at the Institute for Advanced Study in Princeton, New Jersey. He first wished not to leave Sweden, but attempts to find a research professorship in Sweden failed and "the opportunity to do research full time in a mathematically very active environment was hard to resist", so he accepted the offer and resigned from both Stanford and Stockholm and began at the Institute in the fall of 1964. Within two years of "hard work", he felt that the environment at the Institute was too demanding, and in 1967 decided to return to Lund after one year. He later noted that his best work at the Institute was done during the remaining year.