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 interaction motifs that help to form large macromolecular complexes that may be important for the formation and plasticity of synapses.