The overall task of a liquid-liquid extraction process consists of selectively transferring solutes from a donor solution to a recipient solution through a liquid extractant, with the purpose of purifying the donor solution and/or recovering a valuable solute. Thin layer extraction (TLX) is a novel method to carry out this task, using specialized equipment and temporal modes of operation. In TLX, a minute amount of an extractant that is firmly attached as thin layer to a solid substrate is intimately and frequently brought into contact alternately with the donor and recipient solutions. TLX incorporates the complete extraction/stripping scheme into one single device. Following presentation of the underlying concepts, the structural, design, and operational aspects are discussed. TLX is applicable on a wide range of scales and can be easily scaled up to production floor size or down to the microscale. It has inherent operational, safety, and environmental qualities. (c) 2008 American Institute of Chemical Engineers.