Cotton production on the Texas High Plains is limited by water, thermal energy and soil available nutrients. Field experiments have been conducted over a five year period relating lint yield to the integrated effects of each of these limitations. A multiple regression model has been developed which defines the integrated response of the cotton crop to water and nitrogen availability within the constraints of availability heat unit accumulation. The nitrogen supply should be a constant ratio of the water supply for maximum growth and water use efficiency. A ratio of 0.225 kg Na ha^-1 mm^-1 of water was found to produce the greatest water use efficiency defined as yield per unit available water. Using this constant ratio of N:H₂O supply, the relationship between water supply and available heat units was developed. In an 'average' year (1250 heat units, base temp = 15 C), cotton lint yields in excess of 1250 kg ha^-1 are possible on the Texas High Plains. This yield reduction requires 200 mm of water during the vegetative period and 400 mm during the fruiting period for a total of 600 mm. This volume of water is approximately what the average irrigated farmer has available and uses. Dryland yields are very dependent upon the rainfall especially that during the early fruiting period (July). Nitrogen application following a rain during this period greatly increases yield and water use efficiency. By maintaining a proper ratio of N:H₂O, yields can be approximately doubled compared to current yields within the limits of the available water supply and thermal energy.