Sustaining and, most likely, increasing the rate of investment in agricultural R&D worldwide will be crucial to substainably meeting the future growth in demand for agricultural output. However, there are substanatial lags between investing in R&D and realizing a return on these investments, although the R&D effects are typically long lasting.  To place the agricultural R&D spending-productivity growth relationship in a proper, long-run context, new evidence on investments in public and private agricultural R&D in the OECD countries over the past 40 years will be presented and discussed.  Global agricultural R&D spending trends will also be presented along with counterpart, long-term trends in global agricultural production and productivity performance. The overarching theme is to put agricultural R&D in the context of reemerging global food security concerns and provide new perspectives on the changing public and private sector research roles.