The general steady-state theory of eddy-current coupling is extended and new material included. The differences in operation between salient-pole and inductor-type eddy-current couplings are shown and the limitations of inductor couplings emphasised. The peak torque of the inductor coupling is shown to be roughly half that of the Lundell machine and to occur at a much higher slip, giving considerable difference in low-slip performance. Tests taken on an experimental model, which are given in some detail, are shown to verify the theory. The appendix discusses the optimisation of eddy-current couplings of all types, based on the theory given in the paper. This gives the best airgap configuration for maximum low-slip torque, taking into account saturation and the presence of a parasitic airgap. The best pole shapes for torque production are also derived.