Over the past 50 years and longer, the supply of food commodities has grown faster than the effective market demand, in spite of increasing population and per capita incomes. Consequently, the real (deflated) prices of food commodities have steadily trended down. The past increases in agricultural productivity and production, and the resulting real price trends, are attributable in large part to technological changes enabled by investments in agricultural R&D. A range of evidence indicates a slowdown in the long-term path of agricultural productivity growth. A slowdown in the long-term rate of growth can be difficult to discern in the context of myriad other secular and random changes, and even more difficult to attribute among potential causes. It seems likely that at least some of the recent slowdown in productivity growth is attributable to shifts in agricultural R&D spending: a progressive slowing down in the growth rate of total spending on agricultural R&D and a redirection of the funds away from farm productivity that began 20–30 years ago. The effects of a productivity slowdown are cumulative and enduring with potentially serious consequences. Regardless of what caused the slowdown in productivity, a restoration of past growth rates is likely to require an acceleration of spending on farm-productivity-oriented R&D.