In the past decades, significant progress has been made in the neural stimulation and recording technologies. Nevertheless, the majority of the devices available to date have been developed to primarily interface with brain circuits, and there is a technological gap for neural recording and modulation in the spinal cord. This is potentially due to the complex neurophysiology, and inhomogeneous and flexible structure of the spinal cord that impede the development of neural probes and future spinal neuroprosthetics. The latter may, in principle, allow for restoration of motor and sensory functions in paralyzed patients. Advances in optical neural interrogation tools have recently enabled cell-specific neural stimulation compatible with concomitant recording of neural activity. Thus it is highly advantageous to create flexible multifunctional neural probes that can conform to the spinal cord geometry and mechanical properties, while providing optical stimulation and neural recording. We mimic the fibrous and flexible structure of the spinal cord and fabricate all-polymer fiber probes that consist of a polymer waveguide and silver nanowire-coating as electrodes. The polymer fiber probes exhibit low-loss light transmission 1-2 dB/cm. The conductive polymer composite electrodes exhibit tip impedance 100s k½ suitable to record single neuron activity. The mechanical properties of the integrated devices match those of biological tissues, which is difficult to achieve with traditional electrode materials such as metals or doped silicon. We demonstrate the utility our devices for recording and optical stimulation in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, we find that optical stimulation of the spinal cord with the polymer fiber probes induces on-demand limb movements. Finally, we illustrate that the modest dimensions 50-100 _m and high flexibility of our devices permit chronic implantation into mouse spinal cords with minimal damage to the neural tissue.