In the past decade neuronal plasticity has become a major theme of modern neurobiology, from cellular and molecular mechanisms of synapse formation in worms and insects to behavioural recovery from strokes in elderly humans. For this reason the focus of interest in the present volume of Progress in Brain Research is on the topic of neuroplasticity in mature organisms, including humans. Contributions range from neurogenesis and synaptic plasticity in the adult primate brain, to neural mechanisms of learning and memory, and the influence of environmental factors and aging on the functional potential of the central nervous system.