Glutamate is the most important excitatory neurotransmitter in the central nervous system which is involved in synaptic transmission, brain development, synaptic plasticity, learning, and memory. Normally, the enzymatic destruction of glutamate does not occur in the synaptic and extracellular space, but glutamate is removed through specific transporter proteins, leading to stabilization of glutamate concentration at non-toxic levels. When extracellular glutamate concentration increases, it could cause excitotoxicity and lead to many diseases of the central nervous system such as neurodegenerative disorders and multiple sclerosis (MS). Trans-glutaminase enzymes produce large quantities of glutamate by deaminating glutamine and consequently activating immune cells, especially lymphocytes. These activated lymphocytes release glutamate abundantly in the lesion location. Also, the expression level of glutamate specific carriers is decreased in the lesion area. This review discusses on the synthesis and release of glutamate, the natural cycle of glutamine/glutamate and glutamate receptors and transporters, and their role in excitotoxicity and finally their relationship with MS.