microstructural effects should play a major role on the time-dependent dynamics of the polarization switching. [23][24][25] Most commonly, asymmetric electrodes exist in ferroelectric capacitors either because of different metals are used or because the nature of the corresponding metal/ferroelectric and ferroelectric/metal interfaces is different. Thus, asymmetric polarization switching for the positive and the negative bias can occur, as experimentally observed. [22,[26][27][28][29][30] When referring to the resistive switching controlled by ferroelectric polarization, the same arguments given above suggest that the HRS-to-LRS and LRS-to-HRS processes could also be different, implying an asymmetric response when reversing the polarity of the writing electric fields. Understanding and controlling these effects are pivotal to exploit the potential multistate of the ferroelectric memristive device. Even more, a detailed knowledge on the resistive switching dynamics is crucial for ferroelectric tunnel junction's implementation in neuromorphic circuits, where time-dependent action potentials trigger the synapse responses. [31] In the particular case of ferroelectric tunnel barriers, Chanthbouala et al. [17] pioneeringly reported on the impact of the polarization switching dynamics on the measured change of resistance (so-called electroresistance, ER, or tunnel electroresistance, TER). These authors observed that under a given voltage bias larger than the coercive field (at a given measuring frequency) the switching from LRS to HRS was gradual, expanding along a range of voltages. The smooth transition from LRS to HRS was successfully modeled by assuming the contributions of domain nucleation and expansion mechanisms on the domain dynamics. In contrast, the reverse process (HRS to LRS) was observed to be more abrupt. This observation, reminiscent of the asymmetric polarization reversal in ferroelectric capacitors, [22,26,[28][29][30] may imply a different responsivity of LRS and HRS to external stimuli, thus impacting the memristive response depending on the sign of the biasing electric field.Here we focus on the comparison of the resistive transition from LRS to HRS and HRS to LRS in BaTiO 3 (BTO) ferroelectric tunnel junctions, triggered by electric fields of different polarity. We show that the dynamics of polarization and the concomitant resistive switching of the BTO junctions are radically different for both polarizations. The resistive transition from LRS to HRS is smooth, suggesting it is dominated by random nucleation and growth of polar domains. In contrast, the HRSto-LRS transition displays avalanche-like features which depend on the amplitude and frequency of the applied electric field. WeThe resistive switching associated with polarization reversal is studied in detail in ferroelectric BaTiO 3 tunnel junctions, with focus on the dynamics of the ferroelectric domain switching. It is observed that the transition between the high-resistance state (HRS) and the low-resistance state (LRS) is largely asymmetri...