Neurotransmitter transporters of the SLC1 and SCL6 family are found on presynaptic neurons and on glia cells. The function of these transporters is the termination of neurotransmission by the rapid removal of the neurotransmitter molecules from the synaptic cleft. These transporters couple substrate transport to ion gradients of sodium and chloride. Almost all of the eucaryotic transporters have been described to function as oligomers. However, the forces stabilizing the oligomeric state are not well understood. No crystal structures of eukaryotic transporters are available, but recently crystal structures of bacterial homologs thereof have been solved: GltPh (SLC 1 family) was found as a trimer, LeuT (SLC6 family) was crystallized as a dimer. These homologous crystal structures allow rationalizing on the driving forces that stabilize the eukaryotic counterparts.