Molecular and cellular cognition is a new field whose goal is to derive molecular and cellular explanations of cognitive phenomena, such as learning and memory. This chapter is focused on experiments in this young field that tested the role of synaptic plasticity in hippocampal-dependent learning and memory. Besides experiments documenting changes in synaptic function during learning, most of the evidence supporting a role for synaptic plasticity in memory comes from experiments that either enhance or lesion synaptic processes. Since 1992, mouse knock-outs and transgenics have provided compelling evidence that the molecular mechanisms responsible for the induction and stability of synaptic changes have a critical role in the acquisition and storage of information. There is compelling evidence that besides their role in learning and memory, these mechanisms play a critical role in a number of psychiatric disorders such as schizophrenia, age-related cognitive decline, depression, and drug abuse.