A key question in cellular neurobiology is how neurons target molecules to cellular microdomains at a distance from the nucleus. Of special importance are the thousands of postsynaptic sites that form the basis for synaptic communication. Recent evidence suggests that an important aspect of molecular trafficking involves differential sorting, selective intracellular transport, and docking of particular mRNA molecules and associated protein synthetic machinery at postsynaptic sites. This offers the potential for local regulation of the production of key proteins in response to conditions at individual synapses. This article reviews what is known about the mechanisms of mRNA trafficking in neurons and in other cells ranging from oocytes to oligodendrocytes, and considers the possible role that mRNA trafficking and the resulting local synthesis of particular proteins may play in cellular function.