scholar, he emigrated to the United States in 1955 becoming a citizen in 1959. He became a professor at MIT and later at New York University. He served as director of the Courant Institute of New York University in the period of 1967–1970. In 1970 he declined the offer of a chair at the Institute for Advanced Study in Princeton. After 1980 he was at ETH Zürich, becoming professor emeritus in 1995. He was director (sharing office with Armand Borel in the first two years) of the Forschungsinstitut für Mathematik at ETH Zürich in 1984–1995, where he succeeded Beno Eckmann. He led a rebuilding of the ETH Zürich mathematics faculty. Moser was president of the International Mathematical Union in 1983–1986. Research In 1967, Neil Trudinger identified a new function space embedding which could be viewed as a borderline case of the Sobolev embedding theorem. Moser found the sharp constant in Trudinger's inequality, with the corresponding result often known as the Moser–Trudinger inequality. Elliptic and parabolic partial differential equations In the late 1950s, Ennio De Giorgi and John Nash independently discovered the fundamental elliptic regularity theory for general second-order elliptic and parabolic partial differential equations, in which (unlike the Schauder estimates) no differentiability or continuity is assumed of the coefficients. In the 1960s, Moser identified a new approach to their basic regularity theory, introducing the technique of Moser iteration. He developed it for both elliptic and parabolic problems, and beyond recovering De Giorgi and Nash's results, he was able to use it to prove a new Harnack inequality. In his original work, a key role was played by an extension of the John–Nirenberg lemma. Enrico Bombieri later found an argument avoiding this lemma in the elliptic case, which Moser was able to adapt to the parabolic case. The collection of these regularity results are often known as De Giorgi–Nash–Moser theory, although the original results were due solely to De Giorgi and Nash. Differential geometry In 1965, Moser found new results showing that any two volume forms on a closed manifold are related to one another by scaling and pullback by a diffeomorphism, so that geometrically the total volume is the only invariant of a volume form. He was able to apply the same techniques to symplectic forms, thereby proving that a cohomologous family of symplectic forms are related to one another by diffeomorphisms. Moser also analyzed the case of manifolds with