This book introduces the fundamental principles of hydrogeology, focusing on groundwater flow, aquifer properties, and water resource management. The book covers the hydrologic cycle, groundwater-surface water interactions, and contaminant transport. It emphasizes methods for groundwater investigation, modeling, and sustainable management. Practical examples and case studies illustrate hydrogeological concepts and applications. The goal is to equip students and professionals with the knowledge to manage groundwater resources effectively and address related environmental challenges.