Neuronal self-avoidance, or isoneural avoidance, is an important property of neurons which consists in the tendency of branches (dendrites and axons) arising from a single soma (also called isoneuronal or sister branches) to turn away from one another. The arrangements of branches within neuronal arbors are established during development and result in minimal crossing or overlap as they spread over a territory, resulting in the typical fasciculated morphology of neurons (Fig 1).In opposition, branches from different neurons can overlap freely with one another. This propriety demands that neurons are able to discriminate “self,” which they avoid, from “non-self” branches, with which they coexist. This neuronal self-recognition is attained through families of cell recognition molecules which work as individual barcodes, allowing the discrimination of any other nearby branch as either “self” or “non-self”.Self-avoidance ensures that dendritic territories are covered completely and yet non-redundantly guaranteeing that branches achieve functionally appropriate coverage of input or output territories.Neuronal communication requires the coordinated assembly of axons, dendrites, and synapses. Therefore, self-avoidance is necessary for proper neuronal wiring and postnatal development and, together with Neuronal tiling (heteroneuronal avoidance), is a crucial spacing mechanism for patterning neural circuits that results in complete and nonredundant innervation of sensory or synaptic space.