Abstract : An analysis of non-reciprocal directional coup lers and their application in traveling-wave resonant (TWR) circuits is presented. The gen eral characteristic of this type of coupler is determined from an examination of its scattering matrix. One result of interest is that it is not necessary that there be a pi/2 phase differ ence between the output waves of the coupler resulting from a single input wave. This phase difference is necessary for symmetrical couplers. One type of non-reciprocal directional coupler is examined, and the various elements of the scattering matrix are related to its physical parameters. The non-reciprocally-coupled TWR circuit is analyzed for steady state and tran sient behavior, with and without the presence of reflections in the closed loop of the circuit. It is demonstrated that a variable non-reciprocal coupler can serve three functions simultaneously: (1) isolate the power source from amplified ring reflections and hence permit stable tuning of the circuit; (2) isolate the ring from the waves reflected from the dummy load; and (3) act as a variable coupler which is needed to tune the circuit. From the manner in which the non-re ciprocal character is permitted to occur, it is conjecturt it is not possible to devise a TWR circuit which makes use of any arrangement of 4-port directional couplers of any type which can store in the forward-ring wave all the energy supplied by the source.