The electrodialysis method using ion-exchange membranes has been widely accepted for an established industrial technology for the concentration of sea water, but some crucial problems remain. One is the decreased resistivity of membranes associated with well regulated structures, and another is achieving high selective permeability of membranes for respective ions. Recent advances in materials science could offer some useful solutions to these problems. In this article, these problems are discussed in light of the current state of science and technology.