Drought is unique among spells of weather; it creeps upon us gradually, almost mysteriously, but its consequences are a terrible reality. In many instances the damaging effects of drought on the vegetation are not fully realized until it is over. The semiarid and arid lands which make up the greater part of the grazing areas of the world are subjected to protracted periods of deficient precipitation and hence decreased production of forage. It is a common practice for grazing lands to be fully stocked on the basis of the average or better season before a drought. Consequently, if grazing is not immediately reduced in proportion to the decline in forage production, there will be heavy overgrazing with subsequent injury to the forage species. The deterioration of many grazing lands began during protracted drought periods. There generally is no problem in managing the range resource during the wetter years. The years of less than average precipitation set the pattern of land use, and must be anticipated and planned for safe utilization of the range.