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World demand for food is growing and it has been estimated that a 50% increase in crop yield is required to meet the increasing demand due to the growing world population, a situation that is further exacerbated by the predicted variation in climate. Photosynthesis is the process by which plants use the energy from the sun to convert carbon dioxide (CO₂) from the atmosphere into carbohydrates and other chemical compounds, which are used for growth. In order for leaf photosynthesis to take place CO₂ must enter the leaf through adjustable pores, called stomata, and at the same time water is lost through these pores which also aids in cooling of the leaf. As stomatal behaviour controls photosynthesis, water loss and leaf temperature these pores are an unexploited but important targets for manipulation to improve crop productivity. Stomata open in response to increasing light, however this response depends on the wavelength of light, and generally two different responses have been identified. The first is named the “red” light or mesophyll response, occurs at high light levels and is linked directly to the rate of photosynthesis. The second is the “specific blue” light response, which occurs and is saturated at light levels too low to drive photosynthesis. This means that stomata are often more open than they need to be to achieve maximum CO₂ uptake for photosynthesis, and therefore the ratio of carbon gain to water loss known as Water Use Efficiency (WUE) is reduced.  Here we have examined stomatal sensitivity to blue light in a number of species including wheat to explore the potential to optimise the crop’s resource use, thereby maintaining photosynthetic rates while using water more efficiently. We discuss a number of non-transgenic approaches to using the information to produce crops that are more water use efficient.  A second strategy we are also exploring is the speed of stomatal responses to changes in light intensity. As stomatal responses tend to be an order of magnitude greater than photosynthetic responses this can lead to periods of reduced assimilation due to slow stomatal opening and increased diffusional constraints as well as periods of unnecessary water loss by slow stomatal closure when the photosynthetic rate has dropped. Both of these approaches have the potential to increase plant WUE and assimilation rate both of which are critical for plant performance.