Although the scientific literature on drug metabolism is extensive, it suffers from the disadvantage that the material is diffuse and consists largely of specialist monographs dealing with particular aspects of the subject. In addi­ tion, although there are a few excellent texts on drug metabolism in print, these tend to be earlier publications and hence do not take into account the many recent advances in this area. Our motivations for writing this book therefore arose from the clear need for a recent and cohesive introductory text on this subject, specifically designed to cater for the needs of undergraduate and postgraduate students. Much of the subject matter in this text is derived from various courses on drug metabolism given at the University of Surrey and the University of Glasgow to basic science students in pharmacology, biochemistry, nutrition and nursing studies, to pre-clinical medical students and to under­ graduate and post-graduate students in toxicology. Therefore, it is our inten­ tion that this text will serve as a primer in drug metabolism to a variety of students in the life sciences taking courses in this subject. The term 'drug metabolism' in its broadest sense may be considered as the absorption, distribution, biotransformation and excretion of drugs. To cover all these facets of drug metabolism in a single text is a voluminous task and therefore we have focused primarily on the biotransformation aspects of the subject.