Glutamate receptors mediate a vast array of processes in plants, animals and bacteria. In particular, the ionotropic glutamate receptors (iGluRs) are the most abundant excitatory neurotransmitter receptors in the mammalian central nervous system. Because these proteins are constructed from distinct folding domains, most of which can be traced to bacterial precursors, the analyses of these important receptor proteins has been performed on a variety of levels ranging from atomic structure and dynamics to behavioral studies. This review will focus on the structure and dynamics of iGluRs, with particular emphasis on the role that the glutamate-binding domain (S1S2) plays in receptor function.