This review discusses the development and use of drought indices in the United States. Drought is a complex phenomenon affecting various sectors, including agriculture, water supply, and ecosystems. The American Meteorological Society categorizes drought into four types: meteorological, agricultural, hydrological, and socioeconomic. Meteorological drought is defined by a prolonged period of below-normal precipitation, while agricultural drought affects crop yields. Hydrological drought impacts water supply, and socioeconomic drought relates to the imbalance between supply and demand for economic goods. The review highlights the evolution of drought indices, starting with early measures like the accumulated precipitation deficit and the Munger Index, which focused on drought duration. The Palmer Index, developed in the mid-20th century, became widely used as it incorporated antecedent precipitation, moisture supply, and demand. It was based on a water budget model and was used to assess drought severity. However, the Palmer Index has limitations, such as its applicability to specific climates and its sensitivity to calibration periods. Other indices, such as the Standardized Precipitation Index (SPI), were developed as alternatives. The SPI is a dimensionless index that measures precipitation deficits and is applicable across various regions. It is calculated using historical data and normalized probabilities. The SPI allows for the assessment of drought severity, magnitude, and duration across different time scales. The review also discusses the development of other drought indices, such as the Keetch-Byram Drought Index (KBDI) for wildfire monitoring and the Surface Water Supply Index (SWSI) for Colorado. These indices are used to monitor drought conditions and inform drought response actions. The review concludes that while the Palmer Index was a significant advancement, newer indices like the SPI offer more flexibility and applicability across different regions and time scales. The development of drought indices continues to evolve, reflecting a better understanding of drought's complex nature and its impacts on various sectors.This review discusses the development and use of drought indices in the United States. Drought is a complex phenomenon affecting various sectors, including agriculture, water supply, and ecosystems. The American Meteorological Society categorizes drought into four types: meteorological, agricultural, hydrological, and socioeconomic. Meteorological drought is defined by a prolonged period of below-normal precipitation, while agricultural drought affects crop yields. Hydrological drought impacts water supply, and socioeconomic drought relates to the imbalance between supply and demand for economic goods. The review highlights the evolution of drought indices, starting with early measures like the accumulated precipitation deficit and the Munger Index, which focused on drought duration. The Palmer Index, developed in the mid-20th century, became widely used as it incorporated antecedent precipitation, moisture supply, and demand. It was based on a water budget model and was used to assess drought severity. However, the Palmer Index has limitations, such as its applicability to specific climates and its sensitivity to calibration periods. Other indices, such as the Standardized Precipitation Index (SPI), were developed as alternatives. The SPI is a dimensionless index that measures precipitation deficits and is applicable across various regions. It is calculated using historical data and normalized probabilities. The SPI allows for the assessment of drought severity, magnitude, and duration across different time scales. The review also discusses the development of other drought indices, such as the Keetch-Byram Drought Index (KBDI) for wildfire monitoring and the Surface Water Supply Index (SWSI) for Colorado. These indices are used to monitor drought conditions and inform drought response actions. The review concludes that while the Palmer Index was a significant advancement, newer indices like the SPI offer more flexibility and applicability across different regions and time scales. The development of drought indices continues to evolve, reflecting a better understanding of drought's complex nature and its impacts on various sectors.