In this article, we examine the relationship between public investments in agricultural research and development and the productivity-enhancing benefits they generate. Knowledge productivity functions are estimated for U.S. agriculture using data on multifactor productivity and public knowledge stocks. We examine the time-series properties of the data and compare alternative econometric estimation procedures. The results are used to calculate economic performance measures such as internal rates of return and benefit-cost ratios. The real rate of return to public investments in agricultural research and development in the United States is in the range of 8–10% per annum.