Neurons are defined by their remarkable polarity, a feature that is highly conserved across most nervous systems. A key neuronal structure, the axon initial segment (AIS), is essential for establishing and maintaining a functional, polarized neuronal architecture. As such, defects in the AIS and a loss of polarity are associated with neurological dysfunction and numerous disease states. Though critical for fundamental aspects of neuronal polarity and synaptic transmission, we have lacked the tools to define the molecular choreography that endows the AIS with such important functions until recently. My work has spearheaded approaches to visualize and uncover the dynamic cell biology at the AIS in both cultured mammalian neurons and living C. elegans animals. I will present our findings on how active cellular mechanisms at the AIS maintain neuronal polarity and drive nervous system function, bridging cellular and developmental neurobiology with the behavior of living animals.