An exciting area of multiple sclerosis (MS) research has been advances in the understanding of leukocyte trafficking and the potential for targeting this area for therapeutic intervention. In particular, there has been a great deal of interest in the molecules that control trafficking of specific lymphocyte subsets into various tissues. Because of the accumulation of lymphocytes in the central nervous systems (CNS) of patients with MS, this has been an area of active investigation that is of interest to neuroimmunologists and clinical neurologists.