Abstract: An electrodialyzer for desalinating an aqueous solution comprises a plurality of parallel chambers (5, 6, 7, 8) formed alternately of anion exchange membranes (3) and cation exchange membranes (2, 4) arranged in a non-linear flow path the aqueous solution so that the solution passes successively across a surface of each of the membranes. The two end chambers (5, 8) house an anode (9) and a cathode (18) connected to a source of electrical bias (11) and this causes ions to form and to migrate from the flow path into a concentration chamber (6) separated from the flow path by membranes (2, 3) from which the concentrated fluid can be drawn off. A process is also described for desalinating aqueous solutions.