Hair analysis is a reliable and widely used tool to evaluate drug exposure in many fields, including workplace testing, drug abuse history and withdrawal control, post-mortem toxicology, doping control, therapeutic drug monitoring of pharmaceuticals and even environmental exposure to toxic agents. Compounds incorporated into the hair structure resist hair growth and regular washing for several months, leading to a potential chronological trace of exposure, with farther periods corresponding to the hair segments more distant from the hair root. The relentless improvement of analytical procedures and instrumental technologies, together with the continuous introduction of new psychoactive substances, have led to an increasing number of studies and practical applications of hair analysis. This book is a comprehensive guide to hair analysis from general concepts, ideal for students and those new to the field, to interpretation and advanced methods for experts working in the area. With contributions from world-leading scientists in each field, this book describes state-of-the-art, emerging issues and recent analytical approaches to hair analysis that will serve as an essential tool to clinical and forensic toxicology laboratories across the globe.