Magnetic resins provide a means of exploiting the advantages of continuous moving-bed ion exchange. These advantages include small resin inventory, compact plant and tolerance of suspended solids. Magnetic ion exchangers can be handled conveniently at small (< 100 mu m) diameters and therefore offer high reaction rates. Their ability to be pumped without significant attrition simplifies plant design. Magnetic devices can also be used for resin handling. The review outlines the synthesis of resins containing a range of magnetic fillers and having various geometries, including uniform spherical, core-shell and ＇plum pudding＇ structures. Kinetic studies and their consequences for plant design are described. Magnetic ion exchangers have been used for pilot-scale treatment of potable water and industrial wastewater in compact and fluidized moving beds. The largest plant built to date is a 1 ML/day fluidized-bed desalination plant, but very large flows can be treated in mixer-settlers.