The targeting of AMPA- and NMDA-type glutamate receptors to synapses in the central nervous system is essential for efficient excitatory synaptic transmission. Recent studies have indicated that protein—protein interactions of these receptors with synaptic proteins that contain PDZ domains are crucial for receptor targeting. NMDA receptors have been found to bind to the PSD-95 family of proteins, whereas AMPA receptors interact with the PDZ-domain-containing protein GRIP (glutamate receptor interacting protein). PSD-95 and GRIP contain multiple PDZ domains as well as other protein—protein interactions motifs that help to form large macromolecular complexes that may be important for the formation and plasticity of synapses.