This CTR-Special is on one of the most exciting topics in the neurosciences, the regulation of axonal growth during development and in the injured nervous system by attraction and repulsion. How the specific wiring of billions of neuronal connections is achieved in the brain has been of interest since the days of Cajal, and even earlier. The implications of this topic extend far beyond developmental neurobiology into the fields of applied medicine, clinical neurology and related disciplines. Following the discoveries of Eph receptors and their ligands, semaphorins and netrins, the field has greatly expanded in the past 2 years and continues to grow. Much of the current fascination for some of these molecules is related to their ambiguous roles in axonal growth promotion and repulsion.