After receiving his Ph.D., Phelps went to work as an economist for the RAND Corporation. His main interest was macroeconomics, but RAND focused on defense work so Phelps decided to return to the his studies the next year, 1960. He took a research job at the Cowles Foundation, and a teaching job at Yale. At the Cowles Foundation, his research was mainly on future prices and wages, following the work of Robert Solow. As part of this research, Phelps published in 1961 a famous paper on the golden rule savings rate, one of his most important works for economic science. He also wrote papers about other economic theories, such as monetary economics (Ricardian equivalence) and its importance when producing the best economic growth.