Eduard J. Zehnder is a Swiss mathematician, considered one of the founders of symplectic topology.
Zehnder studied mathematics and physics at ETH Zurich from 1960 to 1965, where he also did his Ph.D. in theoretical physics, defending his thesis in 1971 under the direction of Res Jost. He was a visiting professor at Courant Institute of Mathematical Sciences (invited by Jürgen Moser), visiting member of Institute for Advanced Study in Princeton from 1972 to 1974. He passed his habilitation in mathematics in 1974 at the University of Erlangen-Nuremberg. He had appointments at the University of Bochum from 1976 to 1986; at the University of Aix-la-Chapelle during the academic year 1987–88, where he was director of the Mathematical Institute. From 1988, he had a chair at ETH Zurich, where he became emeritus in 2006. He was plenary speaker at the International Congress of Mathematicians (ICM) in 1986 at the University of California, Berkeley. In 2012 he became a fellow of the American Mathematical Society.
He has made fundamental contributions to the field of dynamical systems. In particular, in one of his groundbreaking works with Charles C. Conley, he established the celebrated Arnold conjecture for fixed points of Hamiltonian diffeomorphisms, and paved the way for the development of the new field of symplectic topology.
He directed the thesis of several mathematicians. His first student was Andreas Floer, who defended his thesis in 1984.