N-methyl-D-aspartate receptors (NMDARs) in the rodent hippocampus have been shown to be essential for spatial learning and memory, and for the induction of long-term synaptic plasticity at various hippocampal synapses. In this review, we examine the evidence concerning the role of NMDARs in hippocampal memory processes, with an emphasis on the function of NMDARs in area CA1 of the hippocampus in memory acquisition, and the unique role of NMDARs in area CA3 in the rapid acquisition and associative retrieval of spatial information. Finally, we discuss the data that have emerged from in vivo hippocampal recording studies that indicate that the activity of hippocampal place cells during behaviour is an expression of a memory trace.