Droughts can emerge from multiple hydrometeorological processes that cause deficits in precipitation, soil moisture, and surface and groundwater flow, creating conditions with significantly drier than normal water content or availability. Droughts are generally evaluated using indices linked to meteorological, agricultural, and hydrological phenomena. To manage drought disasters before, during, and after the rehabilitation process, accurate drought characterization is crucial to determine type, severity, and spatial extent. More than 100 drought indices have been developed in the literature to assess drought disasters, incorporating a variety of drivers and parameters. Some indices rely solely on hydrometeorological drivers, others use remote sensing technology, and some employ combined approaches. Understanding the drought phenomenon and analyzing drought indices along with their calculation workflows are essential for researchers in this field. Tracking and applying different drought indices across research studies requires significant time and focus. Therefore a comprehensive review of drought index methodologies is important to identify streamlined approaches and prevent inconsistencies among hundreds of scientific studies. This chapter provides a detailed review of 46 drought indices, evaluating their types and calculation methodologies in a step-by-step manner.