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 counter‐transport (CCT), electro‐electrodialysis (EED), electrohydrolysis with bipolar membranes (EHBM), and catalysis with ion‐exchange membrane (IEMC).