The rotors of permanent magnet dc electric motors have been constructed by a number of means in the past. Perhaps the most popular has been to bond a set of magnet arc segments onto a steel backing. Now, however, a few magnet manufacturers have begun to produce complete rings of radially-oriented magnet materials. Some are isotropic, others anisotropic. These rings have definite advantages (and a few disadvantages) compared with arc segments and other construction methods. The effect of the magnet shape on the performance of the motors is discussed. Magnetic and physical properties of presently available ring magnets are also briefly discussed