The synapse is a specialized cellular junction with an elaborate and highly evolved capacity for signal transduction. At excitatory synapses, the neurotransmitter glutamate is released from the presynaptic nerve terminal and stimulates several types of glutamate receptors in the postsynaptic membrane. These include the ionotropic receptors, which are glutamate-gated cation channels, and the metabotropic receptors, which are G protein-coupled seven-transmembrane receptors. The ionotropic glutamate receptors have received special attention because of growing evidence that changes in their synaptic abundance, posttranslational modification, or molecular interactions can provide long-term changes in synaptic strength. This review summarizes new information about the ionotropic glutamate receptors and relates receptor function to the organization of the postsynaptic membrane and the regulation of electrophysiologic and biochemical signaling at the synapse.