This book is a summary overview of water resource management in the Western United States. The book is organized into three parts, each addressing an important aspect of the subject: Part 1 provides information on natural systems and the basics of hydrology, Part 2 provides an overview of water rights, and the legal concepts that have been adopted to allocate water resources to various uses, and Part 3 provides context for future allocations of water resources by describing influential factors and recent data trends.