Excitatory amino acids (EAA) serve important physiological functions in the vertebrate CNS, including participation in fast excitatory synaptic transmission, modulation of synaptic plasticity and regulation of neuronal morphology during development. However, paradoxically they also harbor neurotoxic (excitotoxic) potential, which, if unleashed, can cause widespread degeneration of CNS neurons. Accumulating evidence suggests a role for excitotoxins in a variety of human neuropsychiatric disorders. This paper reviews the classes of EAA receptors in the CNS, the mechanisms underlying EAA-mediated neuronal damage and the role of EAA in specific human disorders.