While the Consultative Group on International Agricultural Research (CGIAR) has been long considered a driving force behind the successes of the “Green Revolution”, no prior study has attempted to develop an aggregate estimate of the value of the CGIAR System’s impacts. However, economic ex post impact assessments have been conducted for some of the most outstanding individual innovations of the System. This study aggregates benefit estimates from specific technologies, and sets such against total investments in the CGIAR centers, so as to derive estimates for five different aggregate benefit–cost scenarios. Impact assessment has been pursued in a largely decentralized manner by individual research centers, and, as a result, methods and approaches differ among studies. Consequently, a critical review process was necessary for determining the reliability of individual impact estimates. A framework including two overarching principles for evaluating study reliability – (1) transparency and (2) demonstration of causality, as well as accordant criteria and indicators, was developed to assess individual estimates of economic impact before inclusion in scenarios of aggregate benefits. Against an aggregate investment of 7120 million 1990 US dollars, resultant benefit–cost ratios for research to date range from 1.9 to 17.3, depending on scenario. However, the true value of benefits arising from the CGIAR is probably in excess of even the upper bounds of these results, as only a small subset of System impacts have been quantified.