Synaptic connections in the brain are continuously remodeled in response to neuronal activity. This process, known as synaptic plasticity, is widely accepted as the cellular process underlying learning and memory. We now know that an important contributor to synaptic plasticity in the hippocampus and other brain regions is the regulated addition and removal of glutamate receptors at excitatory synapses. In particular, AMPA type glutamate receptors (AMPARs) can be transported in and out of the postsynaptic membrane in a regulated manner, resulting in long-lasting changes in synaptic strength. Despite the importance of AMPAR trafficking for the regulation of synaptic function and plasticity, very little is known of the membrane trafficking machinery that mediates the intracellular sorting and targeting of AMPARs at synaptic terminals. During this presentation, I will describe our latest results that have led us to identify an intricate network of distinct endosomal compartments mediating the bidirectional movement of AMPARs in and out of dendritic spines and the synaptic membrane during plasticity.