This quick-reference guide explains how to conduct sound hydrogeologic studies and prepare solid hydrogeologic reports. The emphasis is on ground water, but pertinent surface-water and soil-water topics are covered briefly as well. It uses figures, tables and case-histories illustrate and summarize main points and to relate them to actual problems. Discusses what geologic and hydrologic data are needed, where to get them and how to compile/present them. Tells what to do with geologic information once it is compiled, focusing on three major categories -- stratigraphy, structure and geomorphology. Addresses what do with hydrologic information once it is compiled --focusing on surface, soil and ground water. Discusses the need for, and make-up of, a sound working model of the hydrogeology of a study area. Reviews the basic components of a hydrogeologic report, outlines a proven approach to any writing task, and provides tips on avoiding common mistakes. Shows how the data gathering, analysis, and report writing apply to specific types of hydrogeologic studies, including case histories, e.g., water supply, ground-water contamination, hydrologic monitoring, mining, ground-water modeling. For hydrogeologists, hydrologists, environmental engineers, environmental scientists, civil engineers, geologists.