The importance of rice-wheat cropping systems in meeting present and future food needs in South Asia is reviewed. Evidence from a number of factor productivity studies, which analyze yield trends after adjusting for changes in levels of input use, suggests that growth in the productivity of South Asia's rice-wheat cropping systems is leveling off and, in some areas, declining. Some probable causes of this disturbing trend are considered, including soil-related factors (depletion of soil chemicals, soil physical problems from puddling soils for rice and/or repeated cultivation for wheat); problems relating to the quantity and quality of irrigation water; continuous and intensive cereal cultivation, which has increased the incidence of pests (including weeds) and diseases; and delayed planting of wheat following rice, a common practice in many rice-wheat systems, which severely reduces wheat yields. Changes in the organization and management of research, which are required to restore growth in productivity, are discussed in the final sections of the paper.