Glutamate is the principal excitatory neurotransmitter in the brain. Glutamate activates cation-selective receptor channels carried by nearly every neuron and by glial cells. Bernd Sommer and Peter Seeburg describe how our concepts concerning the molecular and functional design of ionotropic glutamate receptors are rapidly progressing, with the recent discovery of novel receptor properties and new subunits following the landmark cloning of the first receptor subunit by M. Hollmann and his colleagues. New properties currently revealed by the cloned receptor channels may guide physiologists in characterizing the elementary steps in synaptic transmission, help neurologists to define the role of glutamate receptors in acute and chronic neuropathologies, and enlighten all neuroscientists whose models for learning and memory involve the idiosyncracies of particular channel subtypes.