This paper reviews 74 operational and proposed drought indices to provide a comprehensive overview of drought indices, highlighting their differences and examining trends in their development. Drought is a stochastic natural hazard caused by prolonged and intense precipitation deficits, affecting agriculture, hydrology, and society. Drought indices are quantitative measures that characterize drought levels by integrating data from variables like precipitation and evapotranspiration into a single numerical value. These indices help in drought early warning, monitoring, and contingency planning. There are more than 100 drought indices, including meteorological, agricultural, and hydrological drought indices. The Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Index (SPI) are among the most widely used. The US Drought Monitor (USDM) is a composite index that integrates multiple drought indices. Remote-sensing-based indices like the Normalized Difference Vegetation Index (NDVI) are also used to monitor vegetation health. The paper discusses the development of drought indices, their applications, and the challenges in their use. It emphasizes the need for a comprehensive understanding of drought indices to improve drought management and planning. The review highlights the diversity of drought indices and their evolving nature, reflecting the complexity of drought and the need for adaptive and comprehensive approaches to drought characterization.This paper reviews 74 operational and proposed drought indices to provide a comprehensive overview of drought indices, highlighting their differences and examining trends in their development. Drought is a stochastic natural hazard caused by prolonged and intense precipitation deficits, affecting agriculture, hydrology, and society. Drought indices are quantitative measures that characterize drought levels by integrating data from variables like precipitation and evapotranspiration into a single numerical value. These indices help in drought early warning, monitoring, and contingency planning. There are more than 100 drought indices, including meteorological, agricultural, and hydrological drought indices. The Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Index (SPI) are among the most widely used. The US Drought Monitor (USDM) is a composite index that integrates multiple drought indices. Remote-sensing-based indices like the Normalized Difference Vegetation Index (NDVI) are also used to monitor vegetation health. The paper discusses the development of drought indices, their applications, and the challenges in their use. It emphasizes the need for a comprehensive understanding of drought indices to improve drought management and planning. The review highlights the diversity of drought indices and their evolving nature, reflecting the complexity of drought and the need for adaptive and comprehensive approaches to drought characterization.