Over recent years, we have come to the surprising realization that sensory cortex is highly plastic in functional organization, even in adult brains. Much of the evidence for this conclusion comes from studies of the effects of peripheral deafferentation or sensory experience on the somatotopy of primary somatosensory cortex (area 3b) of monkeys. Local modifications in cortical representations occur rapidly after sensory loss or more gradually during altered sensory experience. These changes depend on reductions in lateral inhibition and other dynamic adjustments in sensory networks, as well as Hebbian-like modifications of synaptic strengths. Activity-dependent alterations in the expression of neurotransmitters and modulators may also play a role. After major deactivations, such as those produced by amputation or section of dorsal column afferents, cortex regains responsiveness over a much longer time period as a result, at least in part, from the growth of new connections.