An electric motor-generator has a rotor (1), a stator including soft ferromagnetic cores (3, 5) and coils (4, 6), permanent magnets (2) having pole axes in a plane radial to an axis of rotation of the rotor, means for mounting the magnets, the cores and coils to the rotor and stator, and means for energizing the coils. The rotor is caused to rotate by attraction of the magnets to the cores (5) as the magnets and cores approach one another, an opposite attraction force between the magnets and the cores being neutralizeable by energizing the coils (6) as the magnets and cores move apart. The cores are C-shaped and a magnetic circuit is formed when the magnets and cores are in proximate alignment.