Of all the faculties of mind, memory is the one that contributes most to our sense of self. For over a century it has been assumed that memory is stored as changes in the strength of connections between nerve cells in the vast neural networks of the brain. This process, known as synaptic plasticity, is widely studied in a brain region known as the hippocampus. In this talk I will describe some of the experiments that have led to our current understanding of the molecular machinery of memory. I will focus on how the brief activation of one class of L-glutamate receptor, the NMDA receptor, triggers long lasting changes in synaptic transmission mediated by a different class of L-glutamate receptor, the AMPA receptor, during the forms of synaptic plasticity known as long-term potentiation (LTP) and long-term depression (LTD). The role of various signaling molecules, such as Ca2+ and the protein kinase GSK-3b, will be described. The potential roles of aberrant synaptic plasticity in neurological disorders, such as Alzheimer's disease, will also be discussed.