The development of precise connections in the mammalian central nervous system requires neural activity. Synchronous patterns of afferent activity, and coincident afferent and target activity are required for specifying the neuronal connectivity that characterizes the adult visual pathway in mammals. During development, postsynaptic target neurons communicate with presynaptic afferents. Recent evidence suggests that the mechanisms that underlie activity-dependent development of connections in the visual system may share significant similarities with the mechanisms responsible for synaptic plasticity in the adult brain.