The growth cone at the tip of an extending axon is exquisitely sensitive to repulsive and attractive guidance cues in its environment. These molecules may be diffusible and work from a distance, or may be bound to a membrane or substrate and work at close range. It is the complex integration of these repulsive and attractive signals that enhance or suppress axon outgrowth, and/or guide the axon to its appropriate target. These molecules play critical roles during nervous system development and may regulate the regeneration during nervous system disease.