New uses of artificial selective membranes, particularly ion-exchange membranes, improve on traditional methods of treating liquid mixtures before, during or after chemical or biochemical reactions. With the correct choice of ion-exchange membrane in a membrane reactor, reactions can be performed in such a way that the main product is not contaminated by undesired byproducts. Recent examples, mainly in organic chemistry, are given for eight typical ion-exchange membrane reactors: electrodialysis (ED), electrometathesis (EMT), electro-ion substitution (EIS), electro-ion injection-extraction (EIIE), coupled countertransport (CCT), electro-electrodialysis (EED), electrohydrolysis with bipolar membranes (EHBM), and catalysis with ion-exchange membrane (IEMC).