The generally observed bipolar electrical switching of Cu\CuTCNQ\metal memories (metal=Al,Yb,Ti) between two stable resistance states is shown to occur at the CuTCNQ\metal interface and not in the bulk of CuTCNQ. The switching is explained by a model involving electrochemical formation and dissolution of Cu filaments at the interface. In this mechanism, CuTCNQ acts as solid ionic conductor and source for the Cu+ cations. The model also explains earlier reported findings of bipolar switching in CuTCNQ devices, including the apparently contradictory observation that neutral TCNQ appears in the low-resistance state. (c) 2007 American Institute of Physics.