Paul J. Steinhardt is the Albert Einstein Professor in Science and on the faculty of both the Departments of Physics and Astrophysical Sciences at Princeton University. He is one of the leading theorists responsible for inflationary theory. He constructed the first workable model of inflation and the theory of how inflation could produce seeds for galaxy formation. He was also among the first to show evidence for dark energy and cosmic acceleration, introducing the term "quintessence" to refer to dynamical forms of dark energy. He has pioneered mathematical and computational techniques which decisively disproved rival theories of structure formation such as cosmic strings. With Neil Turok, he introduced the ekpyrotic theory of the universe which is currently the leading competing idea to inflation.