A drought is a period of unusually persistent dry weather that costs long enough to cause serious problems such as crop damage and/or water supply shortages. The severity of the drought depends upon the degree of moisture deficiency, the duration, and the size of the affected area. There are actually four different ways that drought can be defined. Meteorological is a measure of departure of precipitation from normal. Due to climatic differences, what might be considered a drought in one location of the country may not be a drought in another location. Agricultural - refers to a situation where the amount of moisture in the soil no longer meets the needs of a particular crop. Hydrological - occurs when surface and subsurface water supplies are below normal. Socioeconomic -- refers to the situation that occurs when physical water shortages begin to affect people. This book presents leading research from around the globe.