 Cass' doctoral advisor was Hirofumi Uzawa, who also introduced him to Tjalling Koopmans, who at that time was a professor at Yale University.In 1965, Cass graduated with a Ph.D. in economics and statistics with a dissertation on optimal growth, with parts of the dissertation later published in the "Review of Economic Studies".After graduation Cass began to work from 1965 to 1970 as an assistant professor at the economics department of Yale University and as a research associate at the Cowles Commission for Research in Economics in New Haven.