Neurotrophic factors control the survival and differentiation in developing neurons. Furthermore, recent evidence suggests that neurotrophic factors promote the axonal growth and synaptic plasticity in the CNS. Research is currently being undertaken in order to determine whether members of the neurotrophic factor family have potential therapeutic roles in preventing and/or reducing the neuronal cell death and atrophy. This review summarizes the current knowledge of characterized neurotrophic factors including NGF, BDNF, NT-3, and NT-4/5.