Prepared by the Atmospheric Water Management Standards Committee of the Standards Development Council of the Environmental and Water Resources Institute of ASCE Guidelines for Operational Hail Suppression Programs, ANSI/ASCE/EWRI 39-15, describes the process for designing, conducting, and evaluating operations to suppress the formation of hail. Hail is the product of vigorous, deep convection in the atmosphere. The most common approaches to hail suppression involve seeding a storm with nucleating agents using airborne, ground-based, or rocket and artillery delivery systems. Although the effects of seeding clouds for hail suppression are not fully understood, five concepts are commonly employed in successful projects: beneficial competition, early rainout, trajectory lowering, promotion of coalescence, and dynamic effects. The standard covers the design of hail suppression operations, including a definition of project scope, selecting a seeding agent, delivery methods, meteorological data collection and forecasting, selection and siting of equipment, legal issues, and environmental concerns. It also considers important factors in conducting a hail-suppression program, including the operations manual, personnel requirements, operational decision-making, communications, safety, and public relations. Finally, it describes approaches to evaluating the project area and measures to evaluate effectiveness using both direct and secondary evidence. A glossary and references are included. Standard ANSI/ASCE/EWRI 39-15 uses the best available scientific and technical knowledge to describe a process that optimizes the likelihood of success. It will be of interest to hydrologic engineers, meteorologists, agricultural producers, property insurers, and other interests vulnerable to hail damage