While still a graduate student, he began teaching at Cornell University, remaining there until 1979, when he retired from Cornell and accepted a new position as Miller Research Professor in the Department of Statistics and Mathematics at the University of California, Berkeley.
While still a graduate student, he began teaching at Cornell University, remaining there for many years and eventually becoming Horace White Professor in 1973. In 1979, he retired from Cornell and accepted a new position as Miller Research Professor in the Department of Statistics and Mathematics at the University of California, Berkeley.