Excitatory amino acid receptors are the mediators of synaptic transmission at many synapses that can undergo use-dependent modifications of synaptic efficiency. They also play an essential role in the induction of these plastic changes. Graham Collingridge and Wolf Singer describe how NMDA receptors can endow synapses with hebbian-like properties and discuss how these may be used by vertebrates for associative learning and experience-dependent modifications of synaptic connections during development. The role of AMPA receptors in the maintenance of long-term potentiation is also discussed.