Book excerpt: Solvent Extraction in Biotechnology deals with the reco- very and purification of primary and secondary metabolites by solvent extraction. In the first part the reaction engineering principles: definitions, thermodynamic fundamentals, and system models, the kinetics of mass transfer between two phases without and with chemical reaction as well as extraction equipment, which are important for downstream processing in biotechnology, are considered in detail. The special part of the book describes the recovery of low-molecular metabolites: alcohols, acids and antibiotics with organic solvents, carrier-modifier-solvent systems, supercritical gases as well as with liquid membrane techniques. Several practical examples are given for the recovery of different metabolites as well as for the calculation of the extraction processes necessary for equipment design. Besides solvent extraction, novel separation techniques with liquid membrane, microemulsion and reversed micelles are also presented. This book will introduce the biochemical engineer and process engineer to the recovery of products from complex cultivation broths by modern techniques of solvent extraction and help them with process design.