Axon growth and axon regeneration are co-operative processes; the speed and extent of axon growth are influenced both by the properties of the environment surrounding the axon growth cone, and the properties of the neuron itself. In recent years, the environmental influences on axon growth have received most of the attention directed towards this area of research, but the properties of the neurons themselves are likely to be just as important. Within both adults and embryos there are differences in the growth potential of different neuronal types, and there is also evidence for an overall decrease in the vigour of axon growth with neuronal age.