The book is devoted to an important aspect of pharmacology and pharmaceutical chemistry, i.e. the significance of stereoisomerism of drugs for their biological effect from the point of view of their pharmacokinetics, pharmacodynamics and toxicology. The authors review the landmarks in the development of stereochemistry and stereopharmacology. Present-day IUPAC terminology is discussed; general issues of stereoisomerism are considered including separation of racemic mixtures and asymmetric synthesis of isomers, methods of quantifying the isomers of a drug in biological material. The authors put special emphasis on general problems of the influence of stereoisomerism on pharmacological and adverse effects of drugs. A classification of drugs based on stereochemical properties of their isomers is proposed. Possibilities of interaction of stereoisomers in racemic mixtures are discussed. A considerable portion of the book is devoted to pharmacological action of the main groups of drugs whose structure includes asymmetric atoms (that is, drugs with several isomers). Detailed attention is paid to advisability of developing single isomer drugs and to the specifics of their study at the stage of preclinical and clinical trials.