This textbook is developed from lectures for a graduate class in soil-plantwater relations taught at Kansas State University. Students in the class are from a number of departments, including agronomy, biology, horticulture, forestry and recreational resources, biochemistry, and biological and agricultural engineering. The book can be used as a text for a graduate- or upper-level undergraduate courses or as a self-study guide for interested scientists. The book follows water as it moves through the soil-plant-atmosphere continuum. The text deals with principles and is not a review of recent literature. The principles covered in the book, such as Ohm’s law and Poiseuille’s law, are ageless.