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The gastrointestinal (GI) tract is essential for the absorption of nutrients, induction of mucosal and systemic immune responses, and maintenance of a healthy gut microbiota. Key aspects of gastrointestinal physiology are controlled by the enteric nervous system (ENS), which is composed of neurons and glial cells. The ENS is exposed to and interacts with the outer (microbiota, metabolites, and nutrients) and inner (immune cells and stromal cells) microenvironment of the gut. Although the cellular blueprint of the ENS is mostly in place by birth, the functional maturation of intestinal neural networks is completed within the microenvironment of the postnatal gut, under the influence of gut microbiota and the mucosal immune system. Recent studies have shown the importance of molecular interactions among microbiota, enteric neurons, and immune cells for GI homeostasis. In addition to its role in GI physiology, the ENS has been associated with the pathogenesis of neurodegenerative disorders, such as Parkinson's disease, raising the possibility that microbiota-ENS interactions could offer a viable strategy for influencing the course of brain diseases. Here, we discuss recent advances on the role of microbiota and the immune system on the development and homeostasis of the ENS, a key relay station along the gut-brain axis.