Solid-state electronic devices and biological systems exhibit drastically disparate materials properties. While semiconductor devices are often hard, brittle, and bound to flat wafers, biological electronics, such as our nervous system, are soft, mobile, and three-dimensional. Our group bridges this material divide between synthetic and biological electronics by creating multifunctional fibers capable of minimally-invasive interfacing with the organs while integrating advanced sensing and stimulation capabilities. This talk will highlight the development and applications of multifunctional fibers to recording and modulation of neural activity in the brain and in the gastrointestinal tract in behaving subjects. Finally, it will demonstrate how bioelectronic devices can be applied to uncover neural circuits underlying gut-brain communication, paving the way to future gut-centric therapies for neurological and psychiatric disorders.