To increase crop yield per unit of scarce water requires both better cultivars and better agronomy. The challenge is to manage the crop or improve its genetic makeup to: capture more of the water supply for use in transpiration; exchange transpired water for CO 2 more effectively in producing biomass; and convert more of the biomass into grain or other harvestable product. In the field, the upper limit of water productivity of well-managed disease-free water-limited cereal crops is typically 20 kg ha -1 mm -1 (grain yield per water used). If the productivity is markedly less than this, it is likely that major stresses other than water are at work, such as weeds, diseases, poor nutrition, or inhospitable soil. If so, the greatest advances will come from dealing with these first. When water is the predominant limitation, there is scope for improving overall water productivity by better matching the development of the crop to the pattern of water supply, thereby reducing evaporative and other losses and fostering a good balance of water-use before and after flowering, which is needed to give a large harvest index. There is also scope for developing genotypes that are able to maintain adequate floret fertility despite any transient severe water deficits during floral development. Marker-assisted selection has helped in controlling some root diseases that limit water uptake, and in maintaining fertility in water-stressed maize. Apart from herbicide-resistance in crops, which helps reduce competition for water by weeds, there are no genetic transformations in the immediate offing that are likely to improve water productivity greatly. Media summaryImprovements in water productivity will come from better agronomy and better genotypes tuned to each other so that the combination performs well in farmer's fields.

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'Drought' has many meanings in relation to crop production. These range from: statistical (say, the lowest decile of annual rainfall) to a meteorologist; through yield being limited by too little water to an agronomist; to sudden severe water deficits to many molecular biologists. To a farmer, the corresponding management issues, respectively, are risk management (how best to manage a meteorologically drought-prone farm over several years), how best to match cultivar and agronomic operations to the developing growing season, and how best to minimize possible major damage to (say) floral fertility induced by severe water deficits during flowering. All these definitions and the issues they imply are relevant to improving crop production when water is limiting. How can scientists best help? The answers depend on the scales (temporal and spatial) being addressed. Agronomists and breeders, interacting, can help improve components of seasonal water balance in the field, for example, minimizing evaporative losses from the soil surface by better matching the development of a crop to its environment. Physiologists, biochemists, and molecular biologists can help by identifying ways of improving the competence of particular organs. A promising target is floral infertility resulting from water deficits, which results from lesions in tissue, and cellular and molecular processes. Choosing problems whose solutions will have implications in the field and be attractive to farmers requires knowledge of what is important in the field.