Xenobiotic metabolism is a subject of broad interdisciplinary, encompassing physiology, pathophysiology, pharmacology, toxicology, environmental issues, biochemistry, genetics, medical chemistry, computational (bio)chemistry, analytical chemistry, etc., and reactions of hydrolysis play a central role in metabolic pathways. Benard Testa is very well-known for his capacity to conceptualize reactions of drug metabolism, and, in this volume, he presents a comprehensive review of all metabolic reactions and enzymes involved in the hydrolysis of drugs and prodrugs. Nothing of this sort has been written before, as hydrolysis together with some other reactions of drug metabolism have long been in the shadow of the drug-metabolism communityβs preoccupation with the βP450 hypeβ and the superfamily of CYP genes coding for oxidative enzymes of drug metabolism. Recent developments, such as peptide drugs or inhibitors of cholinesterases, have lent new importance to these βotherβ important enzymes of drug metabolism. Bernard Testaβs fundamental knowledge of this field and his commitment to clear conceptualization and precise language make this book, sadly delayed by the untimely death of Joachim Moyer, another important addition to his contributions that help us to understand the principles of xenobiotic biotransformation.