Dowsing has been a known practice for at least 500 years, with some evidence suggesting it may have been used for millennia. Historically, dowsers used a forked, Y-shaped stick, following the movement toward the presence of water, minerals, or other objects located beneath the ground. Today, the most common tool used is a wire bent into the shape of an "L," leading to the term L-rod dowsing. Only a few of dowsing's many forms appear to have a clear physical basis, such that some physical phenomenon in the environment causes a physiological response in the body. Despite the many studies performed in the past, none have resulted in a comprehensive, testable explanation for how dowsing works.This book reviews and critiques some of the common explanations for L-rod field dowsing, describes an investigation into various aspects of L-rod dowsing, and proposes a mechanism which explains the physical observations. Building on the prior scientific studies, it presents a theory based on well-known scientific principles for the physical component of dowsing.