Grain yield of cereal crops is a function of the amount of water used for evapotranspiration, the portion of evapotranspiration used for transpiration, the transpiration ratio, and the harvest index. The most important factor is the amount of evapotranspiration not only because it is directly proportional to grain yield, but because it tends to also make all the other factors more favorable. Therefore, even small increases in evapotranspiration can be significant. Strategies for manipulating both soil and plant conditions for increasing ET how the amount of ET affects the other factors will be discussed for water deficient areas.